http://s1333.photobucket.com/user/abcdefg12345677/library/?sort=3&page=1
Here's the video. You only need to watch the first 30 seconds as she only does it twice and remember its my ISA Brown not my Leghorn.
I've got a video of my ISA Brown doing something similar. I didn't capture the video myself. I'll post it and tell me if its the same as what your hen is doing. You only need to watch the first 30 seconds of it. She only does it twice.