Looking for a children’s science fiction collection. Only remember one story. It was about a boy who finds an alien or some weird creature in his room, behind a chair I think. He goes to swat it or stomp on it, but it startles him by talking to him, begging for its life. It convinces him it’s friendly. But by the end of the story, it’s clear the creature had malicious intentions; but it’s too late. And the end of the story is the creature telling the boy he should’ve killed it when he had the chance. That’s how I remember it, but I read it 30 years ago.