[michaelnoguera]

Cries logical Bobby to Ned, will you dare

A bet, which has most legs, a mare, or no mare.

A mare, to be sure, replied Ned, with a grin,

And fifty I’ll lay, for I’m certain to win.

Quoth Bob, you have lost, sure as you are alive,

A mare has but four legs, and no mare has five.

- from A Panorama of Wit, 1809, p. 53

[hooli_gan]

Care to explain? I don't get it

[xypage]

They bet on whether a horse or no horse has more legs, guy says a horse duh, other guy says haha but a horse has 4 legs and no horse has 5. This means horses don't have 5 legs so no horse has 5, but also taken very literally "no horse has 5" means no horse has more than a horse, 5 vs 4, so they win the bet.