My grandma started walking five miles a day at age 60.

This joke is a perfect example of misdirection. The setup primes you for a wholesome story about a senior citizen's impressive fitness routine. You're expecting a punchline about her excellent health or her sharp mind. Instead, the joke yanks the rug out from under you by taking the premise to its most literal and absurd conclusion. The humor lies in that sharp, unexpected turn from a story about healthy living into a dark but ridiculous scenario where a woman has simply walked off the map over thirty years.

The joke also plays on the very common, real-world advice for older adults to stay active. Walking is the go-to recommendation from doctors and family members alike. But if you do the math, this fictional grandma has trekked over 54,000 miles, which is more than enough to circle the Earth twice. It’s a hilarious reminder that while following good advice is important, you should probably also let your family know your route.