Plastic Penis
I've just seen the film and I have to say that I am absolutely sure that they used a plastic penis for the "famous" BJ-scene. When she sucks his penis, its skin doesn't move at all. Furthermore, he has his hand on the thing ALL the time as if he wanted to hide something. Why would he put his hand around his cock while she gives him a blow? It doesn't make any sense.
The fellatio is real. I have no doubt. But the penis is definitely fake!