If you walk around the halls of the Capital building or the House / Senate Office buildings, the lobbyist are thick, and they are not hard to spot.

One of the first times I went into the House Chambers there was a representative giving a quite animated speech to a handful of his aids. I asked what was going on and was told that it was for the folks back home. If you watch C-SPAN and see someone giving a speech, and the camera angle never changes, that is what is going on.