so why do the doctors flick the syringes?

I really don't get it.  Does it actually accomplish anything?

It's to clear out air bubbles or something.

yea its to settle the bubbles then they squeeze out the air, injectin air is deadly

To rid the syringe of any air bubbles. Air being injected into your veins is a bad thing.

"I really don't get it.  Does it actually accomplish anything?"

Its to remove any air bubbles within the syringe and to check the needle is not blocked by anything. Injecting air into a vein can cause an air pocket to appear in your heart and that can be fatal. It can also cause a blood clot to appear in your body aswell which also can be fatal.

It causes you to focus more on the needle, and allows you to build up more fear and aprehension about the process than you would have otherwise.

Or...

It's to clear out the air bubbles as others have said.

what everyone else said ^^

air, they will kill u if bubbles get in the bloodstream

air, they will kill u if bubbles get in the bloodstream