Grasses: Strange tastes
The spread of grasses was due to the drying of the climate.
Grass looks simple but it is a very specialised plant. It has tiny flowers that rely on the wind for pollination and its leaves grow from the base and not the tip as with most plants.
So when a fire or grazers damage the grass blades, new ones can grow from the root stocks almost immediately.
Leaf-eating animals from the forest moved out onto the plains to feed on the bounteous grass. But leaves are not easy to digest and a digestive system must work on them for a very long time to extract their nourishment.
Rabbits do this in a surprising way. Having nibbled a stomach full of grass the rabbit retreats to its burrow and excretes special mucus-covered pellets of half-digested grass. As each pellet emerges the rabbit immediately swallows it so that all its food passes through its digestive system twice.