Eagle head

Keeper of The Hornet Forest just appears in the episode: Squidward in Clarinetland. Squidward accidentally encounters this bird chasing SpongeBob, who'd recently stolen his Clarinet. The Clarinetland Bird, upon seeing Squidward, questions Squidward, who in response says that he is looking for his stolen clarinet. The Keeper scoffs at Squidward's plight, and tells him that "a clarinet cannot be owned". He then proceeds to eat Squidward. His head probably just sprouted from the ground unexpectedly.

Looks

The Keeper is simply an eagle head protruding illogically from the ground.

Stomach

The Keeper's stomach is an obvious play on surrealistic dimensions, as it is illogical for him to even have a stomach. Inside leads to several other implausibly placed rooms, the first of which is a mirrored room.