Camouflage: Rolling in the grass can be an instinctual behavior from their wild ancestors. By covering themselves in scents from the environment
Scent Marking: Dogs have scent glands in their skin, and rolling in the grass can help them deposit their scent, marking their territory or leaving their "scent signature" on their favorite spots.
Social Interaction: Rolling in the grass can be a social behavior. When one dog rolls in something interesting or smelly, other dogs might do the same
Masking Odors: Dogs have a highly developed sense of smell, and rolling in certain scents could help mask their own odors from prey or other animals they're tracking.
It Feels Good: Some dogs simply enjoy the sensation of rolling in the grass. The texture and coolness of the grass against their skin can be pleasurable for them.
Stress Relief: Rolling in the grass may provide a sense of stress relief or relaxation for dogs. It can be a comforting and calming behavior.
Exploration: Dogs are naturally curious, and they often roll in new scents or textures they encounter. It's a way for them to investigate and explore their environment.