Mia Wallace's near fatal mistake

Earlier in the movie, Eric Stoltz's character asks "I'm all out of balloons, is a baggie okay?"

Now I am no drug expert but am I to infer that heroin is supposed to go into a balloon and cocaine into a baggie? And Mia Wallace thought that was cocaine and that's why she overdosed?

A friend of mine who knows a lot more about drugs than I do said that's not true, but what do you guys think?

-Anonyous

A Quick Question about Mia Wallace's Hair

After seeing the movie in theaters last night, my friend and I are having a disagreement. Is Uma [Mia Wallace] wearing a wig, or is it a cut and dye?

Thanks!