You all know that the Messages application in iOS displays a small animation when your interlocutor writes a message. Based on that animation, you know that you have to wait to see what he writes before answering, a message surely coming your way. In the idea of helping some to trick their friends, someone he thought to reproduce that iOS animation and publish the image on the Internet in the form of a gif file. Sending that file to a friend will give him the impression that you are writing a message to him and he will wait impatiently to see what you have to say, but of course he will not receive anything.
In this way, you can keep your friends busy with your conversation for a few minutes, until they realize that they will not actually receive anything and that the animation is just an image sent by you. The idea is interesting and if you are curious to test it, all you have to do is to save this image in your iDevice and send it as an attachment to anyone you want to be kept in suspense by a message that will never reach them.
