Splitting found cash with a friend means you now share a secret, and secrets cost more than forty bucks.

Money nobody reported stops being money fairly quickly and turns into something the two of you have to manage. There is a story to keep straight, a flinch whenever the subject comes near, and a debt of silence neither of you actually agreed to carry. The split feels like generosity at the time. What got handed over was an obligation.

If you find cash, try the dull route first: hand it in where you found it, or ask around for whoever lost it. When there is genuinely nobody to return it to, say that openly rather than quietly. Watch any plan whose main feature is that nobody can know.