Hello! I have a black walnut tree in my yard that produced a whole lot of leaves this fall, so I was thinking about using them as a covering for their run. My hope is that they will provide both entertainment and a covering for the cold ground. However I read that black walnuts can be toxic, and cause curled toes? Is that true? I don't want to take any chances, so if anyone has any advice, it would be much appreciated! Thanks!