My friends iguana has a red sac hanging from its rectum what is it?

it was noticed 3 days ago and looks like a umbilical cord attached to a round sac no bigger than a dime but is hangin out about 1.5-2 inches and pulsates with its heartbeat/bloodflow, i read on google of a chameleon having its lining and intestines come out, is this maybe what happened with the iguana? taking it to the vet tomorrow but am surprised what happened... any useful info is appreciated