A.B.
Once my daughter ate a 50 foot piece of floss. She pulled out all the floss from a pack wadded it up like gum, chewed it, and swallowed it.
I called the doctor and they said just let her pass it naturally. If a child ate a long piece of floss then I would not "pull" it out from their behind, but rather trim it with scissors and let them pass it in stages, but if it's a short piece then I wouldn't worry about it at all.