Around the 43-44 minute mark there is a woman's corpse shown with erect nipples. A corpse is unable to have erect nipples due to physiological reasons.
The short text at the beginning says, that the members of the 'Sonderkommando' were killed after 3 months, but this is a simplification of the more complicated history. While it's correct that these men were supposed to be killed and replaced after a few months, in some cases they were killed much earlier and in other rare cases they could survive for over 2 years, like Filip Müller. This depended mostly on the skills of the individual 'Sonderkommando' slave worker, who was sometimes needed by the SS to train the new 'Sonderkommando' members, but also on pure coincidence and luck.