What is the smallest grazing animal to keep in a garden?

[Peter Baird]

not necessarily a goat, something that's friendly and has small poop so it won't stack in the garden, but a goat would be fine if there's nothing smaller

 

[Tom K]

Rabbits would fit your criteria, but doubt they eat enough to control the grass if that's what you want. A Pygmy Goat might be your best choice.