Okay I've always stood on the wings and pulled on the feet, except I usually do it really fast. Like half a second, pfffft, game over.

Never had any problems, done to dozens of grouse.

Now I just heard that you are supposed to 'pull upwards and slowly!' when you do it.

I researched on google and found like 20 different people saying 'pull slowly' yet none of them explain why to pull slowly.

ISO why you aren't supposed to do it fast?