I came upon these "misshapen potatoes" in my backyard. They were growing under a mulch of grass clippings in two small clusters close together, a few of them in each cluster. The one on the picture is 6 cm long, 3.5 cm in diameter, the others were smaller. It feels like made of rubber, the smell is difficult to describe, neither pleasant nor especially unpleasant. Are they kind of Truffles? Sorry for the bad quality pictures.