Whoever let the dog out didn't realize what he was going to do next.
Lex, a 1-year-old puppy, got his head stuck in a hole in a wall and was rescued by Vacaville firefighters early Tuesday morning.
The dog learned "about physics the hard way," department officials wrote on their Facebook page, when he "stuck his head through a dryer vent hole that was cut into the siding of a garage."
A resident and her two children were unable to free the trapped pup and called for help.
Firefighters did not have to cut into the wall and instead helped Lex squeeze out of the hole, after which he promptly scampered off.