The other day I saw a random clip on YouTube, where Alice sneaks up to Bob, who is vacuuming, and scares Bob. Bob gets startled and swings the vacuum into (Bob's own) expensive television, breaking the TV in the process.

It got me thinking if Alice could be liable for damages here and what the respective law would be.

Supplemental: Would anything change, if the TV was actually owned by Alice?


4 Answers 4


I will assume that whatever Alice did to startle Bob was a breach of a duty that she owed to Bob, in order to get to what I see as the more interesting aspect of the question: whether Bob's intervening act removes Alice's liability for the breaking of the television. There are certainly scenarios where Alice might have startled Bob without even breaching a duty, but in that case the analysis would end there.

A startle reaction will almost never sever the chain of legal causation

In negligence, Alice is held liable for harm that is reasonably foreseeable as a result of Alice's breach of a duty. One of the elements of a successful negligence claim is causation: Alice is not liable for harm that is too remote from her breach.

On its own, proof by an injured plaintiff that a defendant was negligent does not make that defendant liable for the loss. The plaintiff must also establish that the defendant’s negligence (breach of the standard of care) caused the injury. That link is causation.1

(Clements v. Clements, 2012 SCC 32, paragraph 6)

Bob's startle response would almost certainly be considered a foreseeable reaction, and thus, not sufficient to separate Alice from the breaking of the television.

An instinctive human reaction, or any non-negligent human action in the chain of causation will almost never break the chain of causation, because such reactions will be held foreseeable; and even if they are not, the precise chain of events leading to an accident need not be foreseeable.

(Ken Cooper‑Stephenson, Personal Injury Damages in Canada (Carswell, 1996))

See also The Restatement of Torts (Second), § 447, which says that an intervening act does not remove the defendant's liability if: "(a) the actor at the time of his negligent conduct should have realized that a third person might so act, or (b) a reasonable man knowing the situation existing when the act of the third person was done would not regard it as highly extraordinary that the third person had so acted, or (c) the intervening act is a normal consequence of a situation created by the actor's conduct and the manner in which it is done is not extraordinarily negligent."

"[I]t is the general nature of the intervening acts and the accompanying risk of harm that needs to be reasonably foreseeable. Legal causation does not require that the accused must objectively foresee the precise future consequences of their conduct." (R. v. Maybin, 2012 SCC 24).

Foreseeability does not require that the intervening action be probable; it only requires that it would not be brushed aside as "far-fetched."

The degree of probability that would satisfy the reasonable foreseeability requirement was described in The Wagon Mound (No. 2) as a "real risk", i.e. "one which would occur to the mind of a reasonable man in the position of the defendan[t] ... and which he would not brush aside as far-fetched"

(Mustapha v. Culligan of Canada Ltd., 2008 SCC 27, paragraph 13).

Examples of intervening acts held to be reasonably foreseeable:

  • Haynes v. Harwood [1935] 1 K.B. 146. A carriage owner had left a two-horse carriage unattended on a busy street. The judge accepted evidence from an independent observer that two boys had come along and one of them threw a stone at the horses and the horses bolted along the street (these boys were not before the court as co-defendants; nothing more is said of them). A constable managed to stop the horses, but was injured in the process. The carriage owner was liable in negligence: a reasonable person should have foreseen that the horses might get loose and someone be injured while trying to stop them. The court said, "it is not necessary to show that this particular accident and this particular damage were probable; it is sufficient if the accident is of a class that might well be anticipated as one of the reasonable and probable results of the wrongful act."

Foreseeability here does not have its colloquial meaning

Greendrake's answer says that "whereas Bob's shock is foreseeable, I pretty much doubt that him breaking the TV is." In my view, this takes too colloquial a view of foreseeability. As Hart and Honoré say in Causation in the Law, 2nd Ed. (1985):

... in one sense everything is foreseeable, in another nothing. The consequences of negligence are almost invariably surprises. All depends on the detail with which the harm is described. ... there will always be some details of the recoverable harm which are not foreseeable.

... the fact that harm described by reference to certain details is not foreseeable does not render the harm, more broadly described, unforeseeable. ... If we have learned from experience to expect a 'rainstorm' on seeing dark clouds, then the rainstorm was foreseeable even if, when it occurs, it has other characteristics (e.g. lasted two hours, covered an area of 40 sq. miles) which we could not foresee but which might appear, ex post facto, in a more specific description of it.

Of course, foreseeability is a question of fact, and I acknowledge that a finder of fact might very well conclude that swinging a vacuum is not within a class of actions that might be anticipated by a reasonable person. While I disagree with Greendrake's analysis and conclusion, the contrast with my answer helps highlight precisely where the issue would be if this were to be litigated.

1. Note the terminology. The breach of the standard of care is the negligence. But liability only follows when the negligence causes harm. This is contrary to the framing in Dale M's answer, which says, "Alice was negligent if her actions caused damage to Bob’s TV," and that "[i]f we are talking about Alice’s TV then there is no negligence because Bob has suffered no damage." That language conflates negligence (the breach) with liability (breach plus causation).

  • Whereas Bob's reaction is foreseeable, I pretty much doubt that him swinging the vacuum is. Why not to reasonably foresee that he would instead drop the vacuum & scream?
    – Greendrake
    Jun 4, 2023 at 14:25
  • 4
    @Greendrake have you truly never seen a startled person turn rapidly around to face the person startling them? Seems unlikely.
    – barbecue
    Jun 4, 2023 at 18:47
  • 1
    With regards to Haynes v. Howard, how is the carriage owner responsible, but the stone-thrower isn't? Or were they both responsible but the stone thrower was never identified?
    – Ryan_L
    Jun 5, 2023 at 4:02
  • "I will assume that whatever Alice did to startle Bob was a breach of a duty that she owed to Bob" certainly makes for a clear answer. But it only covers a subset of possibilities, perhaps those most appropriate to the prank described in the question. She could startle him by accidentally dropping something (to make it more complicated, that could be caused by her tripping over the vacuum cleaner cable!), or just as he suddenly notices she's approached him - with him making so much background noise she could be talking, expecting him to hear, and still startle him when she got close.
    – Chris H
    Jun 5, 2023 at 15:45

I actually remember seeing a similar court case on TV. I'm pretty sure it was Judge Judy, as she went off on the friend, berating about being childish, irresponsible, and was lucky his friend didn't have worse injuries. I don't remember the case exactly, but it goes something like this:

A mechanic was working in his home's garage. The mechanic was working on fixing something and very focused. His friend had arrived unannounced and saw this and decided to jump scare him. His friend snuck up behind the mechanic and and yelled. The friend confirmed this is what happened in his testimony. The scare caused the mechanic to flinch and cut his hand deeply on a sharp piece of metal he was working on. This wound required him to be taken to the emergency room, get stitches, and lose time working at his full time job, due to the injury. The mechanic sued his friend for damages.

The judge said the visitor is liable, as his intent was to provoke the reaction which caused the injury. Had it been purely accidental, there would have been no intent and therefore, no liability.

  • "the visitor" - I'd assume, inviting you into my home indemnifies you from unintentional damages. What do you call horseplay in legalese?
    – Mazura
    Jun 4, 2023 at 19:46
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    @Mazura Im not a lawyer, so I cant speak on it. Im just recalling something similar I saw on TV. Also, I doubt inviting someone in removed liability. If I invite you into my house and you attack me, then thats still on you.
    – Keltari
    Jun 4, 2023 at 20:31
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    It's worth noting that the Judge Judy show is arbitration, not court. Judy is a trained judge, but she's not bound as strictly by legal principles here.
    – MJD
    Jun 5, 2023 at 12:45
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    @MJD That is correct. I had even said in my answer that this was arbitration, but the community edited that out. Strictly following the law or not, it goes to show that a person of authority and a legal background believes intent to be the a major factor - if not THE factor - in determining guilt and liability. Personally, I happen to agree. Everyone knows scaring someone can cause them to jump/flinch/move involuntarily. Intent is the difference between an unfortunate accident and negligence.
    – Keltari
    Jun 5, 2023 at 20:51


The relevant law is negligence.

Most jurisdictions say that there are four elements to a negligence action:

  1. duty: the defendant has a duty to others, including the plaintiff, to exercise reasonable care,

  2. breach: the defendant breaches that duty through an act or culpable omission,

  3. damages: as a result of that act or omission, the plaintiff suffers an injury, and

  4. causation: the injury to the plaintiff is a reasonably foreseeable consequence of the defendant's act or omission.

Arguably, Alice was negligent if her actions caused damage to Bob’s TV.

If we are talking about Alice’s TV then there is no negligence because Bob has suffered no damage.



Bob gets startled and swings the vacuum into (Bob's own) expensive television, breaking the TV in the process.

Swinging things around is quite an atypical reaction for a startled person. You would expect them to scream, shake, drop what they're doing and run away, but not to start swinging erratically whatever they happen to be holding in their hands.

Thus, whereas Bob's shock is foreseeable, I pretty much doubt that him breaking the TV is. Unless, of course, Alice was aware of Bob's propensity to swing things erratically when frightened.

  • 8
    This answer assumes that Bob, when startled, begins randomly waving things around in the air, and completely ignores the fact that Bob is holding a long object (the vacuum) in his hands. It also ignores the possibility that Bob would suddenly turn in the direction of the person startling him without dropping the vacuum. There's no requirement that Bob MUST drop the vacuum when startled.
    – barbecue
    Jun 4, 2023 at 18:44
  • That's of course because all of those "omg lol startled" videos are staged.
    – pipe
    Jun 4, 2023 at 21:22
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    @Greendrake "I'd expect that Alice shows up right in front of Bob to startle him". That's definitely not how you startle someone. It in in fact the antithesis of startling someone. Especially if the startle event causes the startlee to swing around as if to see what startled him.
    – RonJohn
    Jun 5, 2023 at 0:19
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    The entire point is that there is no "correct" or "incorrect" way to be startled. Claiming some prankster doesn't have liability because the victim of a prank got startled the "wrong" way is ridiculous. Startle reflexes show significant variation among different people, but one thing that's universal is there's a NON-VOLUNTARY muscle reaction. That means you CANNOT control it, and CANNOT be held responsible for having such a reaction. In fact, failing to have a startle reaction is an indication of neurological deficit.
    – barbecue
    Jun 5, 2023 at 3:07
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    @Greendrake Nobody is saying it wasn't an accident. But it was a FORESEEABLE accident, resulting from a deliberate attempt to startle Bob. If Alice simply bumped into Bob by mistake and startled him, you'd have a point. But Alice deliberately tried to startle Bob, her goal and intention was to startle Bob. She deliberately planned and executed a series of actions which she KNEW would startle Bob. Your claim that startle reactions are always consistent and predictable is absurd.
    – barbecue
    Jun 5, 2023 at 13:02

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