Emergency rooms are filled with emotion. Every time you get to a really dramatic scene, you just look around and say, OK, that is what my character is doing with her hands. You have all of this physical business to choose from. Plus, you have people calling the taxi after their father has just died of cancer. You have this fantastic stressed language; you're steeping in this incredible stew of emotional reactions.
I think that's brilliant, if a little creepy. But that's what fiction writers do, isn't it? We observe others and we take what we can use: the crooked teeth that show when the homeless man smiles, the way a particular teenager moves as he slouches across the room. We're vultures and proud of it.
Listen to the interview if you have 11 minutes to spare. He tells a hysterically funny anecdote involving fake severed bloody arms about 3/4 of the way through.