Today, many films rely heavily on special effects to help tell their stories. Special effects can be divided into three categories: optical effects, mechanical effects, and the more recent computer-generated imagery, otherwise known as CGI, like from pixar. Mechanical effects typically use things such as props, scale models, and pyrotechnics during live-action shooting. Common mechanical effects include artificial tidal waves and exploding cars. Optical effects are those achieved photographically, either with the camera itself or during post-production processes. A typical optical effect might be a camera shot representing the view of someone peeping through a keyhole. As the name suggests, computer–generated imagery uses computers to create special effects. By making people appear to fly or catch bullets in their mouths, CGI makes the unbelievable believable.