Harley knows that she said something to cause Thor to be holding the fork in such a tight grip. And it is quite difficult for her to monitor what she says, due to the way her mind works. But she is trying to help...

"The friends I made in Arkham were some of the closest I ever had... well, at least until I came to the Nexus."

She reaches forward to put her hand on his, to encourage him to lighten the grip on that fork. "And now I have even more good friends."