Abducted by a mad scientist

Jon was walking home, still thinking about what he would wish for, when all of a sudden, he felt a pain in his neck, and then felt very faint...
He woke up hours later, in a laboratory of some sort. Where is neck met his shoulders felt sore.
He looked up and there was a tall, thin, older gentleman, with greying hair.
"Hello. You, my good, heh, sir, are the product of my latest experiment."
The doctor motioned for Jon to look straight up. Jon did, and what he saw shocked him.
He now had the body of....