Scratch is just a feed or treat that is tossed on the ground that a chicken has to "scratch" and peck to get. It fulfills the need to scratch and peck, keeps them busy, helps trim their claws and beaks. Commercial scratch is typically a mix of whole grains like corn, oats, milo or barley. It can be anything. Berries, oats, crackers, tortilla chips, peas... Just make it work for them to get their fill.