Woof! — Allan Ahlberg

He felt a curious tingling in his hands and feet. He felt his nose becoming cold and wet, his ears becoming flappy.

Eric is a perfectly ordinary boy. Perfectly ordinary that is, until the night when, safely tucked up in bed, he slowly but surely turns into a dog!

What becomes of Eric -- the adventures he has with his best friend Roy, and their joint efforts to puzzle out the reason for his transformation -- makes a very funny and entirely believable book.