For example, if you want to tweet a humorous riff on a certain William Carlos Williams poem, would that actually be legal?
Examples (though I don't mean to single anyone out): https://twitter.com/mathewkumar/status/307557968864489472?s=20 https://twitter.com/sannewman/status/937718586096979968?s=20
The website poets.org includes this copyright notice under the poem
Copyright © 1962 by William Carlos Williams. Used with permission of New Directions Publishing Corporation. All rights reserved. No part of this poem may be reproduced in any form without the written consent of the publisher.