At one point in Rome a slave's testimony against a free person could only be taken under torture (historically this has been proven to not work since at a certain point the tortured will give the torturer what they want to avoid further pain, true or not). In this case this poor girl is the body slave of the Emperor's Mistress who the Empress has plotted to get rid of. The question being asked is "Who did your Domina sleep with last nigh?" They of course KNOW it wasn't the Emperor!
After confessing the poor girl was stuffed in a cell to await the proper time to present her to the Emperor as evidence of his "love's" infidelity.
You guys have no sense of humor when it comes to these things
ps: Historically in many societies while the male ruler could sleep around his consort was in trouble if she did (the whole is this a legitimate heir thingy). Henry the VIII accused Anne Bolyen (wife #2) of charges including adultery, incest and conspiracy against the king. In those days the conviction resulted in the woman being burned alive at the stake (the man was drawn and quartered, hardly a better option). Anne avoided that fate by agreeing to confess to the crimes in exchange for being behead by a sword (which was considered more merciful than being beheaded with an ax which was often botched. Hollywood notwithstanding.)