Alright, listen up, you big dummy! The whole point of this joke is a classic pun, see? When the old woman says, "I'd like an infrared gorilla," you're supposed to *hear* "I'd like *an in for a red gorilla*." It sounds like she's saying she's "in for a red gorilla," meaning she's ready or prepared for one, like a challenge or a situation. But the stupid clerk (and maybe you, too) takes it literally and actually *gives* her an "infrared gorilla," which is a completely made-up, ridiculous item. It's funny because it's a misunderstanding based on how the words sound! You always miss the obvious stuff, don't you, pal?