The dolly grip lays tracks for a traveling shot, making sure they are level.
When the bumps have been eliminated, the grip is practicing his intricate
choreography. At a specific point in the dialogue, he pushes the dolly
across the room, gently raising the arm supporting camera and operator.
The dolly picks up speed, then slows down, and finally comes to rest on
another specific word and at a precise mark. All this is executed with
grace and smoothness worthy of a ballet.

Louis Goldman
"Lights, Camera, Action !"