Testing took place in various places including Spain and Ireland, but beta testers rejected a sixth button with a smiling face with rosy cheeks. Called "yay", the response was apparently more "eh?".
Many users have called for a 'dislike' button, but this idea has been rejected - reportedly because it is thought to be too negative.
"Emojis are the world's fastest-growing digital language, brands including McDonald's, Ikea and Domino's are increasingly using them, particularly to target millennials.