Plot hole: The rape scene in the parking lot... there is no one around for THAT long? But wait, once the detectives come in the scene two people are walking in the background with a shopping cart - they must have seen something!
Plot hole: One scene we are in the alien's (when she is still normal) living space and we can hear through a speaker everything the scientist is saying...wouldn't the alien pick up that something was happening and do something before...?
Answer: Nothing would happen to them. The restriction on sexual activity was to keep them from spreading any potential contaminants through bodily fluids. It's nonsense because there are plenty of ways to spread bodily fluids that don't involve sexual contact and 10 days seems arbitrary, but it fits with the overall erotic themes of the film series to have the quarantine specify no sexual intercourse.
BaconIsMyBFF