Sounds like you partially missed the vein... or you went through the vein and out the other side. Dull needles always seem to do this for swiv, with fresh needles and a little bit of practice its hard to fuck up... He doesn't even pull back the plunger (This is Super dangerous btw, dont take this as advice or a recommendation, shooting speed into an artery will cause gangrene within a few minutes/hours virtually 100% of the time, its hard to do but you will loose some part of ur body to amputation or die if you actually shoot a full dose of speed into an artery)
Anyways he doesn't pull back the plunger because he usually wiggles it around so much attempting to pull it back that it causes scars/bruising. Honestly it does more bad than good for swiv, not to say that one day it might get him killed if he actually shoots into an artery.
It shouldn't hurt at all if you do it right, just a slight sting when you puncture the skin, once ur in the vein nice and good you wont feel much.
If you think shooting speed is a pain in the ass don't shoot coke
... Now thats a hard one to get right, for a newbie.