In his autobiography, T. Boone Pickens relates the story of how he managed to do a deal with a man on his sickbed. He took the contract to the man's house, was shown to the man's room, and handed the papers and a pen to the man.
The man pulled the covers over the paper, pen, and his head, and the papers were signed.
Pickens' lawyer asked him, "Did you actually see him sign the papers?"
Pickens said something like, "No. But I can swear out an affidavit that I handed the papers to him unsigned, and received them back from him signed."
In this case, there is an inference that it was the man, and not a supernatural being that signed the papers. How acceptable are such inferences in a court of law?