It's MIL. AIBU to say something? I was cooking today and Mil was helping out...I finished mashing a load of potatoes and put them in a big bowl. MIL then RAN her finger around the perimeter of the potato and put it in her mouth...as if this wasn't bad enough she then REPEATED the action with the same finger and said fucking YUM!!!!

I was so grossed out. Can someone really get to the age of 65 and think this is ok?
I didn't say anything as we've got history and we're getting on better...should I say something next time and if so what?