 The prelude to mating can be very aggressive , as the male forcefully rams the female 's shell with his own and nips her legs . Mounting is an awkward process and the male must stretch and tense to maintain equilibrium in a slanting position . The concave underside of the male 's shell helps him to balance when straddled over the female 's shell , and brings his cloacal vent ( which houses the penis ) closer to the female 's dilated cloaca . During mating , the male <unk> with hoarse bellows and grunts , described as " rhythmic groans " . This is one of the few vocalisations the tortoise makes ; other noises are made during aggressive encounters , when struggling to right themselves , and hissing as they withdraw into their shells due to the forceful expulsion of air . 
