At the very end when Senator Albinius signals to spare the newly named Spartacus' life he gives the modern thumbs up sign. In ancient Rome the thumbs up sign was to signify the sword being thrust into the heart and therefore death. The closed fist with the thumb against the index finger signified spare the gladiators life. If Senator Albinius had given the thumbs up sign then the gladiator would have been put to death but Spartacus' life was to be spared so the sign was incorrect for the desired result.
One of the naked female dancers at the party has breast implants. Although some forms of plastic surgery were known to the Romans, breast augmentation was not one of them.
During the first battle scene where the Thracians engage the Getae, Spartacus' sword and shield continually change hands with each shot. Throughout the series, the character is shown to be Right handed.