The term 4-D (sometimes 5-D) is used for movies that make use of physical effects inside the theatre, which occur in synchronization with the 3-D movie. These include seats which vibrate, tilt, sway, drop down and rotate, different kinds of smells to suit what’s happening on screen, for example, burning rubber in a car chase; rain, smoke, wind; strobe lights, water sprays and jets and even mechanical ticklers for the legs and arms!
A 4-D experience can be had only in special theatres which are built to produce the effects. There are movie theatres like these in many countries including India (Chennai, Mumbai, Delhi etc).
Ten films, including Avatar, Kung-Fu Panda and the third sequel to the Pirates of the Caribbean have additional 4-D effects.
Picture Credit : Google