In Super Mario Bros. 3, you come across tons of shelled enemies, which you can pick up and carry around. Throw them at question blocks, and they reveal their contents for you.

But, if you take your favorite shell up to a block, and get real close to it (without touching it)

And then let go of your shell, it'll hit the block, and then bounce back toward you

but it'll sail right through you without causing any damage!

And you might be saying "So what? I could just throw the shell at the block from further away and achieve basically the same thing." And you'd be right, you could do that. But this way, you don't have to dodge anything when it ricochets off your target.