I may have accidentally swallowed a piece of dental floss. what could happen?

It comes out: It comes out the other end, out the butt. Do not look for it to come out, but just presume it does. Really, do not go looking for the piece of floss.

No worries: No worries, most likely stomach acids will dissolve the product and you will pass what is left

Not much: It should pass without incident.

No worries: The piece of dental floss will digest and it should pass in your stools within a 24 hour period.