Dynamic Duo

HI all, @facanimi, to add to @Joseph45 comments, this can only be done on a mobile device.  So if you are using one, you need to go to your settings button on the bottom left part of your game.  Click on the pink settings button and then click on the red button.  You should get a settings box that pops up.  Scroll down to "Features" and click on it.  And there it is!