It's not a laugh, it's a cackle.
She's evil and ruthless and cruel, and he's sitting here wondering when he can get out of her cold-eyed gaze that seems to bruise him.
It's funny because he can't ever say anything about all of this to her, because if he did, she'd break and crumble, fall into pieces that he would have to put back together - because he's the black cat.
The cursed animal that has to do her bidding, no matter how much he hates her - the one who always rides on the back of her broom. And here he is - screeching and flailing because she's picking off fur for a spell.
The bitch has no sympathy. Then again, why would she? Her skin is green and full of warts; her life has been turned upside-down.
And now he's the entertainer, forced to sing and dance for her personally. Stuck on the back of her broom as she dangles him back and forth on the string she's attached him to, wrapping him ever so daintily around her finger.