shot for The Black Dahlia
with a rainmaking rig, a sprinkler system used to create the appearance of rain—a common practical effect
A practical effect is a special effect produced physically, without computer-generated imagery or other post production techniques. "Special effect" is often synonymous with "practical effect". In contrast, visual effects are created in post-production through photographic manipulation or computer generation.
Many of the staples of action movies are practical effects. Gunfire, bullet wounds, rain, wind, fire, and explosions can all be produced on a movie set by someone skilled in practical effects.
Christopher Nolan is a modern filmmaker noted for his preference of practical effects over computer-generated effects. Many of the effects used in his action films, including The Dark Knight and Inception, are practical.
Practical effect techniques 
- The use of Prosthetic makeup, animatronics, puppetry or suitmation to create the appearance of living creatures.
- Miniature effects, which is the use of scale models which are photographed in a way that they appear full sized.
- Mechanical Effects, such as Aerial rigging to simulate flight, stage mounted gimbals to make the ground move, or other mechanical devices to physically manipulate the environment.
- Pyrotechnics for the appearance of fire and explosions.
- Weather effects such as sprinkler systems to create rain and fog machines to create smoke.
- Squibs to create the illusion of gunshot wounds.