This was an example question from the mod post on relaxing the "no example seeking" rule, but I actually got curious when I read it. Most of the existing/already asked questions about twins on this subreddit seemed to be about choosing heirs between twins, but there didn't seem to anyone else asking about much else related to twins.

I'll admit I'm particularly interested in twin girls, since anecdotally I've heard some cultures consider twins in general, or twin girls in particular, to be bad luck. But I'm curious about perceptions of and explanations for twins in general, too.

(I especially would like to know how baby twins were told apart. Today, if there's a potential or accidental mix-up, parents can just check hand or foot prints against the birth certificate. How did parents untangle twin mix-ups before the normalization of birth certificates and foot prints?)