My dad tried to explain why we don't eat the turkey's legs.

This joke gets its chuckle from a delightful blend of absurdity and childlike logic. The humor primarily springs from the idea of a roasted turkey, which is very much no longer alive, needing its legs to escape an oven a whole year later. It's a classic example of anthropomorphism, giving an inanimate (or at least, very dead) object a very human-like desire for self-preservation and the means to achieve it. The setup leads you to expect a practical or traditional reason for avoiding the legs, like them being tough or less flavorful, but the punchline delivers a completely fantastical and impossible scenario.

In the real world, turkeys are a staple of holiday feasts, particularly Thanksgiving, and the legs are often a prized part of the bird for many diners. The dad's explanation playfully subverts the reality of holiday cooking, where the turkey's fate is sealed long before it hits the table. The joke leans into that innocent, whimsical kind of reasoning you might hear from a kid, where the boundaries between reality and imagination are a little blurrier, making the punchline unexpectedly silly and memorable.