At dinner, Annji sits next to Scott. When she comments that he might be infected, he is wearing a black t-shirt, but when he responds he has a large red napkin covering his shirt.
The group makes three mistakes with the injections, which Anji's medical training should have prevented. First, Tony, the father, injects his intravenously, which the vast majority of vaccines should not be, and one ought to assume a mystery vaccine without instructions should not be. Second, they sterilize the hypodermics in boiling water rather than alcohol, evidenced by the steam rising from the bowl, but the heat risks damaging the medicine. Third, nobody swabs their skin with alcohol, which prevents infection at the injection site.
The prop hypodermic needles do not even retract to mimic a needle sliding into the skin.