Some ferrets with diarrhea will strain until the soft pink lining of the rectum gets pushed through the anal opening. This tends to happen mostly with young ferrets suffering from proliferative colitis and you should take your ferret to the vet immediately.
A prolapsed rectum which occurs without diarrhea is not something to worry about, unless the ferret starts chewing the prolapse.
It will usually disappear within a day or two but if concerned, take the ferret to the vet.
More information about Prolapsed Rectum in Ferrets can be found on the following sites…
Prolapsed Rectum by Judith A. Bell, DVM, PhD
Photo of a kit with a prolapsed rectum (Miami Ferret)
DISCLAIMER: The information contained on this page is not meant to replace seeing a veterinarian if you think your ferret is ill. It’s only meant to supply general information on a particular illness which was obtained either from personal experience with my sick ferrets, or from books and/or the Internet.