Continuity mistake: During the fight in the corridor of light, Alice shots everybody and there are a lot of blood splattering, but the corridor continues to be clean until the very end, and the stains of blood that are there are not compatible with the splatters.
Continuity mistake: In the opening sequence, while Valentine and her goons shoot the people on the boat, only the exit hole of the bullets is visible, but no entry hole on the white shirts.
Revealing mistake: When Ada Wong kills three officers in the Umbrella Central Control Room, you can see she shot them from the front. They are sitting behind glass panels. Later, we can see the blood splatter sitting on their side of the glass, indicating that they were shot from behind. The glass is also intact, despite a bullet supposedly passing through it.
Continuity mistake: In the scene when Ada Wong walks into the Umbrella control room and kills all the agents, she stands in the middle of the room. She uses a gun to kill all the agents, who are sitting behind glass computers. In that scene, and in later shots, we can see that the glass is intact and has no bullet holes in it.
Continuity mistake: In the 3D map scene both of the teams are heading to the central suburbia section to rendezvous; however when it shows their movements on the map both teams are walking away from this area, back the way they just came from.
Continuity mistake: In the corridor fight scene, the camera shows Alice shoot a zombie in the head, and very shows a bullet entry and exit point. In the next show however, the wound has disappeared.
Continuity mistake: When housewife Alice is trying to escape with her daughter in the laundry room, she slams a mop through the ceiling. When she slams the mophead through the ceiling the last time and pulls it out, the hole left behind is maybe one foot across. When she lifts her daughter up into the hole it is now a good two or three feet across and reaches from ceiling support beam to support beam.