Why did Bud put a rag over the fish heads?

After Todd, Bud's new foster brother, wakes him up by shoving a pencil up his nose, the two get into a fight; enraged by this, Mrs. Amos decides that she will send Bud back to the group home and make him spend the night in the shed in their backyard. 

A very scared Bud is sent out to the shed and locked in by Mr. Amos. Bud looks around and thinks that he sees three "little flat monster heads" (actually, just fish heads!) hanging on the door; their round, bright yellow eyes are the only thing in the shed that aren't gray, and they appear to be staring right at Bud. Their mouths have very sharp, pointy teeth and "lips smiling back ready to bite." Bud panics, feeling that the shed is shrinking around him and that those frightening mouths are closing in on him. Thus, Bud puts a rag over the fish heads to comfort himself, reasoning that this way, "I couldn't see them and they couldn't see me."