Problem with heel hooks is once the knee is stabilized there is very little...'VERY LITTLE' movement in it. Ligament damage happens almost immediately so one must be very careful. That is why reaping the knee is an auto D.Q. in most tournaments. The person receiving must tap quickly and the person doing the heel hook will feel as though they had not done much. When we drill heel hooks and toe holds we stop as soon as there is control and no cranking. Position, Control, Release.
The thing is you are ok. No pain, just a little pressure is felt and POP!!! The damage is done.
When defending...As Soon as you realize there is even the possibility of a heel hook turn your knee outward and pull out. Other wise TAP.