Snap Gum
When a piece of gum is pulled out, the spring inside releases, snapping the victims finger, hence the name "snap gum". Because this gum is spring loaded, it can be used over and over.

The Snappy gum trick (or "snapping gum trick") is a prank wherein a victim is offered a stick of chewing gum from an ordinary-looking chewing gum package. The package, however, does not actually contain gum. Instead, the stick of gum actually has a spring-loaded snapping mechanism. When the victim pulls on the stick of gum, the spring releases and strikes the victim's finger, causing minor pain and embarassment