4D film or 4-D film is a marketing term for an entertainment presentation system combining a 3D film with physical effects that occur in the theatre in synchronization with the film. Effects simulated in a 4D film may include rain, wind, strobe lights, and vibration. Seats in 4D venues may vibrate or move a few inches during the presentations. Other common chair effects include air jets, water sprays, and leg and back ticklers. Hall effects may include smoke, rain, lightning, air bubbles, and smell.