I'm a T2 diabetic, so I'm well aware of the importance of checking your feet - especially the bottom that can be damaged. A lot of diabetics also have a condition called neurotrophy, in which you lose feelings in your limbs (e.g. feet).
My doctor told me about a case many years ago where this guy sat on his recliner and his dog would lick the bottom of his one foot every night. He never thought about it, but when he went in to the hospital for another condition, they found a "hole" the size of a 50-cent piece that went to the bone.
He had to have plastic surgery to fill the void...