When Marcy is going to give an injection to Boyd, the flicks the syringe with her finger, which jostles any air bubbles to the top which are then expelled by pushing the plunger down. After tapping the syringe, Marcy pulls back on the plunger, which draws in more air and can cause a deadly air embolism when injected IV.
After injecting a woman, Grant says it was a bee that also stung him. But bees, unlike wasps, never sting more than once. Two bees, however, might sting two people.
When Mac injects the flight attendant during their yoga class, it seems impossible that no one in the class would notice. At a minimum, the class leader, who is facing everyone else, would have seen what he did.
When Marcy explains the R0, she mistakenly says "incubation period" (the time it takes a virus to mature to full illness) instead of "infectious period" (the time period a virus is able to be transmitted to others).