Blow the heck out of your friends with this hidden thunder gun!
Don't forget to set the command block to repeat by clicking on the button Impulse 2 times. The command block button will then read 'Repeat', and it will turn purple when you exit the interface. Bury the block 2 blocks deep and place one block that isn't redstone or glass, then a pressure plate. Anyone who steps on this plate will be smitten down by a rapid-fire of lightning.
*headphone warning* Prank responsibly! This trap is EXTREMELY loud, since 3 thunderclaps a second are right on top of you!