You can actually improvise a lot as a voice actor. It's not that entirely different than shooting a live action movie; the characters mouths are quite easy to manipulate once all the information is built into the computer. So you can improvise a lot and it doesn't matter really how far along they are in the process they can really just make the character say something different.
Seth RogenI watched a lot of pot movies before we did this [Pineapple Express]. My favorites were always the characters in movies that weren't necessarily in stoner movies.
Seth RogenThe scene with Danny [McBride] and the cake and all of that [in the Pineapple Express], most of that is improvised, I would say. But you would never know, to me anyway, and that's what is always amazing.
Seth Rogen