"A social networking system user may associate an emoji representing the user's emotional reaction with a content item presented by the social networking system. The user is presented with one or more emoji maintained by the social networking system and selects an emoji for associating with the content item."
[1] http://www.google.com.ar/patents/US8918339
That's right folks, they patented using the emoji to respond to content.
On the other hand, I think the patent is invalid because LINE predates this like a year or so.
That's pretty bad.
They say you lose the license if you make a claim "...that any right in any patent claim of Facebook is invalid or unenforceable." They also helpfully indicate what a claim means, and making an assertion counts.
Now why would they do this? My guess is that they wanted to have a legal tool that they could use to provide a chilling effect on any third parties who might volunteer information that is useful to someone filing a lawsuit against them. Which, if you are a lawyer, might seem like a good response to the demonstrated ability of groups like groklaw to crowdsource legal research. And if they were in such a lawsuit, that comment is exactly what Facebook would not want to see.
But there is no need to speculate. Their patent grant is quite clear, and the comment I pointed at is in violation.