SOMETHING ELSE THAT HASN’T SURVIVED into adulthood is the kid-concept of “blood brotherhood.”
It works like this: Two boys (did girls ever do this?) make an incision or a pinprick on their thumbs, then rub the wounds together. “Now we are blood brothers,” they will intone (if they intone anything at all, which they also may not). It’s an expression of intimate friendship; a ritual of bonding with what’s-today-called one’s BFF. And not to be entered into lightly.
I don’t know how old is this gesture is, or even if, in this hazardous fluids-aware world of ours, it is still practiced.