Happily lying down these  cows appear to be doing nothing, but actually they are doing something very important. They are ruminating. This means that the grass they have eaten over the last few hours is being regurgitated from the rumen to have a good chewing in the mouth before being swallowed again . This is  very efficient way of digesting grass and means that cows can produce an average of 20 litres per day almost entirely from grass!