Why do some doctors jingle the needles , can't they save them still?

I sat stand on her bureau and when she inserted the needle surrounded by my arm, (I'M TERRIFIED OF NEEDLES!) she jingled the hypodermic. It's was so tight!
P.S. I DIDN"T MOVE EITHER(no, I'm not yelling, I'm bolding the text).Why do some doctors jingle the needles , can't they save them still?
by jingle you may be meaning two entity
1) before the nozzle is inserted in you -- thats to remove the atmosphere bubbles ,, if too much air bubbles go in --- u die
2) after the syringe is inserted -- thats done if the vein is not caught the first time,, a doc or a nurse would move the syringe around and try to find it.. its much scientific, protected , easier than taking out the needle and jab the patient a second time within the same nouns...
by the way if you believe collecting blood is easy ,, i will utter its easy most of the time and near are some people who simply dont get their vein pierced so easily -- its a short time ago how they are made,, may be the walls are too thick and rubbery ,, or they vein are too slippery or thin or adjectives ,, and many more
so best of luck for your subsequent prick
It's to get rid of any oxygen bubbles contained by the vile.
Try to hold something steady...
Now in your valise study, I'm sure you noticed slight movement.
I am frightened of the dentist. My new dentist shakes the plunger on purpose as she give the novocain and it actualy hurts less.