My Grandma keeps finding potato's in her yard, how do they get there?

One day my grandma was out in the dinning room fixing the curtains and she noticed a potato on the ground. Where it was, was strange because nobody could get back there its covered in bushes. The potato's have holes in them like something was eating away at them we think its snails. She has recently started feeding birds, and from the other side of the fence she has noticed rats coming out and getting to the bird seed in the bird feeder...I don't know if that helps, but please help us! we are very confused and want to solve this mystery! Thank you!:) ( theres about 4 potato's)