Having cooked a ton of pork trotters during my life, I can tell you that the pig foot can "pop" because often there is enough fat in enclosed pockets to vent "explosively" with sufficient heat.
I have had this happen when dry roasting them in an oven (incredibly messy with goop sprayed all over the oven)
A "release valve" so to speak will prevent this. I have a big awl with a t-shaped handle that I use to punch through the hooves in a couple of places. I do the same thing with smoked pigs feet, although it is more difficult there is a soft spot in the frog of the foot.
