I tried slow cooking ox tongue - I marinaded it overnight and continued slow cooked it for hours because it just didn't taste right every time I tried it - I've no idea if or how it could be cooked to taste like something edible but honestly the taste and texture was like nothing I've ever had in my life - it was revolting, didn't even try giving it to the dog - straight in the bin. I'd only tried because a friend said they had had it at a Hungarian/Romanian(?) restaurant and it was delicious.
I love liver done in the slow cooker - I do that regularly - so I thought I'd try it.