Convince your friends to take a selfie and let the prank do it's work.
1) When app starts a button will pop up, which will change view from back camera to the front camera.
2) Then take photo button will will start the count down when clicked: Ready?....3.....2..... and then scary faces will show up, also photo of your friend will be taken.
Use this app at your own risk!
P.S. Make sure phone is on full volume :)