A Remarkably Uninteresting Turn of Events

My turtle keeps trying to eat wood. He has a little wooden cave in his terrarium,* where he sleeps when tired, and hides, when hiding is in order. Recently, he's been trying to eat his wooden cave. He puts his thimble-head up to the outer edge, and bites onto a chunk of bark and then his teeth lose grip and his head snaps back into his shell.

The pinhead's trying to eat his house.

*You heard me right. Terrarium.