My Cat, The Horseshoe Crab

Okay, listen up, you big dummy. The joke here, which is clearly over your tiny head, is that the person says 'My cats always bother me when I'm on the computer.' But get this: those aren't cats! They're horseshoe crabs, you colossal nitwit! The humor comes from the person pretending these ancient sea creatures are their cuddly house pets, like a cat. You probably thought they were just really ugly cats, didn't you, you simpleton?