Fans of Batman will be familiar with the batarang, a bat-shaped throwing weapon that Mr. Wayne uses to subdue his foes. In the trailer for the new film Batman v Superman, he uses a variant that can be folded up when not in use. German cool-weapons-maker Patrick Priebe saw it, and decided to make one of his own.
At the heart of Priebe's fan-made batarang are two stainless steel wings/blades – although he tells us that if the thing isn't actually going to be hurled at anything, those could make of something cheaper such as aluminum.
A dual-spring mechanism joins the wings together at a pivot point in the middle, holding them both down. With the press of a button in that middle piece, however, the springs are released and the wings satisfyingly snap open.
As can be seen in the first video below, the thing really does work – particularly on melons. The second video provides more details on how the batarang was made.
Source: Laser Gadgets by Patrick Priebe