What did the zero say to the eight?

This joke is a classic example of visual humor combined with personification. The punchline plays on how we perceive the written form of numbers. When you look at the number eight, especially a handwritten or stylized one, it can easily be imagined as two zeros stacked on top of each other. The thin line or indentation in the middle (Review), where the two loops meet, then takes on the appearance of a belt cinching the "waist" of the number.

The humor mechanism here isn't complex wordplay or irony, but rather a simple, unexpected visual gag. We're used to numbers representing quantities, not having fashion accessories. The joke humanizes the numbers, giving them the ability to observe and comment on each other's appearance, which is inherently silly and appeals to our sense of playful absurdity. It's a lighthearted way to look at something as fundamental as numerals and find a bit of unexpected fun in their shapes.