After the swathed hay sits in the field for a week to cure, it needs to be raked into a windrow and baled. The rake, as shown in the video below, is a series of large vertical disks with fingers on the edges of the disks. It is pulled by a tractor, but the rake itself is ground-driven. It pulls two rows from the swather into one giant pile of hay that snakes around the field. After this step, the baler comes in, picks up the row, and compresses it into hay bales. Unfortunately, I didn't get any photos or video of the baler because they did it in the middle of the night.