To prepare for the scene where Neo wakes up in a pod, Keanu Reeves lost fifteen pounds and shaved his whole body to give Neo an emaciated look.
The opening action scene took six months of training and four days to shoot.
After the lobby shoot-out, the camera pans back, showing the aftermath of the gunfight. A moment passes, and a large chunk of one of the pillars falls off. This was not planned, but was left in for effect.
Carrie-Anne Moss twisted her ankle while shooting one of her scenes, but decided not to tell anyone until after filming, so they wouldn't re-cast her.
Carrie-Anne Moss performed the shots featuring Trinity at the beginning of the film, and all the wire stunts throughout, herself.