Audio problem: When the first bus blows up (the one that Bob was driving) you can hear the explosion before the bus actually blows up.
Continuity mistake: At the beginning of the movie we see Keanu Reeves taking Jeff Daniels "out of the equation" by shooting him in the leg. We realise it's a serious injury as he requires the use of a cane when receiving his medal. However later on in the movie when they move in on Dennis Hopper's home, which takes place the next day, Daniels is part of the assault team and has no cane, no limp and is obviously very mobile.
Answer: Ventilation shafts or roof panels.
Toolio