G.O.B. has a habit of swallowing keys.
G.O.B. struggles to swallow a key for his Prison escape illusion. It takes him a while to finally swallow the key. When he needs to pass the key, he becomes shy and can't perform in his prison cell. The next day he is stabbed by White Power Bill and the key saves him from the knife doing any serious damage. ("Key Decisions")
When Michael and Steve Holt are handcuffed together for the father-son triathlon, Michael asks G.O.B. for a key to release them so he can prevent George Michael from signing up for Army. G.O.B. retches up the key properly in front of them. ("Notapusy")
Marta: I just couldn’t find my keys.
Michael: Well, my brother may have eaten them.From "Key Decisions"
Michael: Just one heck of a trick you ended up pulling in there, G.O.B.
G.O.B.: Truthfully, that wasn’t part of the act. I was actually trying to get the key to come out of my mouth.From "Spring Breakout"