Mysterious large "thumbs up" in facebook chat??

[Yoda]

I was having a conversation with some on facebook using chat, when a large "thumbs up" was sent to me. I asked about it and she says that on her screen it says that i sent it. But on mine it says that she sent it. So if neither of us sent it how the fuck did randomly appear there?!?!
ON MY SCREEN IT SAYS SHE SENT IT TO ME, BUT ON HER SCREEN IT SAYS I SENT IT TO HER!!!

[M]

Well one of you guys sent it and it should be under someone's name, so that's how you would know. One of you probably accidentally clicked it.

EDIT: Must be a glitch then. I guess just test it and see what happens....you should send one again and see if it still says that.