In another thread a couple of months ago was raised the subject of sexualized executions by wild beasts as described by Martial -- and Apuleius, I must add. The re-enactment of Pasiphae and the bull was considered in the commentary on
M. Valerii Martialis Liber Spectaculorum (Oxford University Press, 2006) by Kathleen Coleman, the leading authority on the subject of 'spectacular executions' in Rome. Here it is:
Given that the popularity of Pasiphae's story earned it a place in the stage repertoire under the Julio-Claudians (specifically Nero), our emperor's performance can be interpreted as an attempt to upstage his predecessors: Martial wants us to believe that this time the bull, the woman, and the intercourse were all real. This brings us up against a problem introduced in General Introduction, Section 5: when is a motif a literary conceit, and when does it reflect actuality? The Roman ambition to realize the impossible, combined with scant regard for those human lives that were deemed dispensable (chiefly slaves and prisoners of war), suggests that we have no reason to dismiss the possibility that the bull in the arena really was roused to mount 'Pasiphae': see Coleman (1990: 63–4). But how could this have been staged?
Close observation of the natural world had doubtless acquainted the Romans with the precoital behaviour in ungulates that is known to zoologists by the German term 'Flehmen'. This is defined by Duden as '(meist von Pferden) die Oberlippe [in geschlechtlicher Erregung] hochziehen'. The male manifests this behaviour upon sniffing the urine of an oestrous female. By curling his upper lip he closes his nostrils, thereby forcing the scent that he has inhaled to enter his vomeronasal organ (otherwise known as 'Jacobsen's organ'), whose epithelium (lining) serves as a bed for sensory neurons. He is then stimulated—presumably by sex hormones excreted in the urine—to mount the female. This behaviour is widely documented in ungulates from the American bison to the Armenian wild sheep; for a lucid account see the description of the mating habits of the African buffalo by Sinclair (1977: 102–3). Other Bovidae, including domestic cattle, behave in the same way; for a close-up photograph of a bull curling his upper lip see Hafez (1968: pl. 20A).
Significantly, the female's urine does not have to be immediately fresh, and males who smell deposits of it on the grass are also liable to perform Flehmen. Hence it seems possible that the Romans could have collected the urine of oestrous cows and smeared it on the genitalia of the human victim in the arena. Rather than being strapped directly to the bull, it seems likely that the woman was probably restrained at the appropriate height on a rack or trestle; for a photograph of a blindfolded stallion penetrating an artificial 'vagina' on a wooden apparatus of the appropriate height covered with canvas see Hafez (1968: pl. 20C). In the case of our spectacle successful penetration would have resulted in an ultimately fatal rupture of the woman's uterine tissues, and—depending upon the exact configuration of the rack—she might have been trampled by the bull's forelegs as well; but since the context was presumably comparable to Apuleius' scene, i.e. the execution of a criminal condemned ad bestias, the sequel to the display would in any case be death—if not in the arena itself, then by the sword afterwards.