What is the use of this particular filmmaking tool? ?

i have been interested in film-making since i can remember. i know that there's the lighting, the many kinds of cameras, and all of that stuff. but after all these years, i haven't found out exactly the name of the following item in this picture and what its used for. its the thing that is shown in the camera when... show more i have been interested in film-making since i can remember. i know that there's the lighting, the many kinds of cameras, and all of that stuff. but after all these years, i haven't found out exactly the name of the following item in this picture and what its used for. its the thing that is shown in the camera when the director says, "take one, ACTION!" but i can't google it since i don't know the name of the item. help me please?

here's the picture:
http://img.photobucket.com/albums/v721/xmalicous/cinemasupplies.jpg?t=1227241514
Update: the name of this item would be super helpful lol thanks (:
2 answers 2