Do you want to make a funny joke? 'Monkey in phone' is a perfect way! You can show animation of moving monkey on friend's phone. Monkey will appear suddenly in time which you select. Monkey animation is played on top of other apps, so your friend can use phone normally.
Your girlfriend is afraid o monkeys? You were in Thailand and you like monkeys? Now you can have your own mammal which looks like chimpanzee! You can set transparency of animation and time when it will appear.