tapping(?) the ground

Our Buff Orpington hen is exhibiting behavior that doesn't worry me, but does tickle my curiosity. My husband noticed it once when he was feeding her some bread crumbs on the patio (away from the flock, and away by choice). The 'tapping' behavior seemed to occur when a flock of birds 'threw' a shadow when flying over. Only this afternoon I was able to watch that same behavior when we were feeding her some bread crumbs (again, away from the flock, but this time inside the outside coop (covered)). I don't know if the 'away from the flock'-part plays some kind of role, but it's sort of weird seeing her tap the ground like that but also interesting at the same time. She sort of perches to the ground (over her piece of bread (as if she is protecting it)), and she starts to tap the ground (both feet in turn) like a bird mimicking a rain shower to make the worms surface. Apart from that, she seems to be healthy. Regular laying behaviour, smooth egg shell, normal droppings, she grooms, etc.
I've been searching the Internet for 'tapping' etc. but maybe I just don't know the right English word for it (being (fresh) from the Netherlands). Hope you can help me, or provide me with a url, or the right word for this behavior so I can do another Google-search.
Thanks up front!