The angle at which Virginia's chair sits, as she goes into the kitchen.
Virginia fires a pistol until it's empty, then we hear two clicks. These clicks would be heard if the gun were a revolver, as the barrel rotates and the hammer falls on an empty chamber. A semi-automatic pistol would not make a sound, as the slide would be stuck in the open position as would the hammer.
When Virginia calls the information desk to find out the LifeWorks phone number, they give her the number 555-4621. But the business card shown at the beginning of the film has a completely different phone number.