Why do people wrap tape around their arm when they shoot up heroin?

I'm not. Are you crazy? I wouldn't touch heroin with a ten foot pole. Heroin took my mother from me. I'd sooner die than I would even consider using it.

I was watching a movie though and there's a scene where a guy does that. He wraps a length of tape around his arm and then pulls it taught with his mouth before sticking the needle into his vein, and I was wondering why he did that.

@BlueMetalChick: Hey hey be nice I was just asking a question. Yes I know your mom passed away I did not remember how she passed away.

@updown2020: Sorry. I guess I get a little aggressive with that.

@BlueMetalChick: It's okay I understand not everyone is out to get you or to make you remember things you rather forget,