Dogs have scent glands all over their bodies, including in their paws, ears, and anal glands.
Dogs are territorial animals, and they will often mark their territory by rolling in grass. This helps them to let other dogs know that this area belongs to them.
Dogs can also roll in grass to cool off. The grass helps to absorb heat from their body, which can help them to stay cool in hot weather.
Sometimes, dogs will roll in grass simply because they have an itch that they need to scratch. The grass helps to remove the dead skin and hair that can cause itching.
If a dog has rolled in something smelly, they may roll in grass in an attempt to hide their scent.
Some dogs simply enjoy the feeling of rolling in grass. The grass feels good on their skin, and it can also help to release endorphins, which have mood-boosting effects.
Rolling in grass is a natural behavior for dogs. Some experts believe that it may be a way for dogs to mask their scent from predators, or to attract mates.