It is amazing to watch, and yes that poor fox cub is very underweight. OH makes a point that I mustn't feed him. But yesterday when Jameson killed a mouse, I chucked the mouse over to our neighbours garden when the fox was there. He absolutely loved it, and started playing with the dead mouse, chucking it around. It was probably a nice meal for him..
I do keep a close eye on them when they interract, but I obviously can't do that 24/7. I hope they all know their place and that Jameson is the boss.