Prank your friends with a virtual Ouija.
In the first field, "PETRUS PLEASE ANSWER ME THE FOLLOWING QUESTION:" shall allways be written.
In the second field, write the question you wanna make to Petrus.
In the first field, no mather what you write, "PETRUS, PLEASE ANSWER ME THE FOLLOWING QUESTION" will appear. In this first field you have to write the answer to the question you are gonna ask in the second field and end it with a point (.) When entering the point at the end, Petrus´ answer will be what you secretly wrote in the first field and your friend will be really shocked. When your friend asks for your phone to try it, he wont know the point trick, so when he makes a question, Petrus will answer in a negative or agressive way, making the trick only work with you.
Be sure to first mentalize your friend, tell him you discovered a very strange app, so he believes it. Also write fast your answer so he doesnt realize you entered something different than "PETRUS PLEASE ANSWER ME"
This is a fun prank for friends or family that can scare more than one... How far you take it is up to you...
This is the best scary prank for Aprils Fools Day.