If they fail to find a vein, repeatedly, on the same arm, the arm in question will end up being rather sore afterward.
I may know this from experience. Experience from today, let’s say. I won’t name the place because I am in a good mood, despite my arm-as-pincushion.
But yeah, the right arm, from which blood was successfully drawn, feels pretty much normal. The left arm feels like it’s been stabbed multiple times. Which it was.
Do not recommend.