[bryanthompson]

http://en.wikipedia.org/wiki/Staple_(fastener)
The staple breaks from the end of the strip and the legs of the staple are forced through the paper. As the legs hit the grooves in the anvil they are bent to hold the pages together. Many staplers have an anvil in the form of a "pinning" or "stapling" switch. This allows a choice between bending out or in. The outward bent staples are easier to remove and are for temporary fastening "pinning". Most staplers are capable of stapling without the anvil to drive straight leg staples for tacking.