An Android and WhatsApp bug is going around that on touch (text selection) will freeze the WhatsApp app for a few minutes. Its a fun bug involving lots of unicode characters that tell the device to render text left to right, then right to left many times over. Tom Scott on youtube who has done a lot with unicode including a real life emoji keyboard knows more then most about what is going on. So check out the video below and see how the bug happens, and maybe even subscribe to Tom Scott for more interesting videos like this and on interesting places around the world.
You can read the Unicode Bidirectional Algorithm linked in the video at http://unicode.org/reports/tr9/.