The same federal agency that once determined that a piece of shoestring is a machine gun has now brilliantly determined than a device to launch soda cans and tennis balls is in violation of the National Firearms Act of 1934.

can cannon
The ATF has absurdly determined that a device to launch 12 oz. soda cans is in violation of the National Firearms Act of 1934.

What is this “dangerous” bit of technology?

The Can Cannon.

Thank, you, ATF, for saving us from the threat of people who might want to have fun.