system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do people flick and squirt needles before giving injections?

This might be a movie/film industry only thing (I don't remember a nurse doing this before I received shots). But why do they do it? It seems like they're squirting/wasting quite a bit of medicine out before giving it to the person.
gpt
You don't want to inject air.

It's difficult to fill a syringe without having at least a small air bubble. Putting the needle up and flicking will get any air bubbles in the syringe up to the end, you then push out the bubble and you know when it's all out of the needle when liquid flows through.

Even when you're not injecting it into a person, if the volume measurement needs to be very precise you won't want any air in there to throw it off.

EDIT; Note that the movie version with a large fountain of medicine coming out is dramatization, but the practice is real and much less wasteful.