Visto la mia preoccupazione iniziale, ho fatto un bel po' di ricerca e dopo aver esaurito le fonti italiane ho iniziato con quelle inglesi, e finalmente credo di aver trovato la risposta al mio problema; la posto qui per avere anche i vostri pareri.
In pratica quella cosa che fuoriesce dalla mia tartaruga dovrebbe essere il pene.
I dettagli sono riportati di sotto(in inglese) e sono stati presi nella seguente pagina
http://www.sulcata-station.org/faq.html; non e' altro che una risposta data ad una domanda simile alla mia da un esperto.
Domanda:
My tortoise seems to have what looks like intestinal tissue sticking out of its rear end! He doesn't seem to be in any pain and it usually goes back in after 15

seconds. The tissue is about 3-4 inches long and grayish/ pinkish/ purplish in color.
Risposta:
Sulcata Station's response: Congratulations -- it's a boy! The tissue extruding from his back end is actually his penis. He is starting to "show off" because he is in the process of reaching sexual maturity.
With reptiles, sexual maturity depends much more on the size of the animal, and not necessarily the age of the animal (with mammals, it's the the other way around -- age tends determine sexual maturity, not size). Male tortoises in captivity tend to reach sexual maturity much earlier than their wild counterparts, simply because captive tortoises are better fed and grow faster.
Male torts display their penises for a variety of reasons. Usually these displays are extremely brief, lasting for a few minutes at most, after which the penis generally goes right back inside the cloaca. This is all very normal behavior for a male sulcata.
The only time to be concerned is if the penis stays out for a long time (say, for more than a day). If it stays out for a long period of time, the tortoise might have a "prolapsed" penis. A prolapse can cut off the circulation to the penis, causing cell and tissue damage. If you suspect a prolapse has occurred, you should take your tortoise immediately to a reptile-competent vet so that the vet can gently replace the penis back into the cloacal cavity.