some studing a lil from here and a lil from there....
Your eyes are what is called a symphatic nerve, im sure everyone knows that if one of yer eyes shut down you have good odds that the other one will to, this is symphatic nerves in action.
Another symphatic nerve is our jaw muscle, these symphatic nerves react to what our body does. When u drop mdma sert. floods the brain giving off "pleasure" to us. We feel so good that our symphatic nerves react in "pleasure" as well. i.e. eye wiggle and jaw clenching
Same thing when you bust a nut you notice yer jaw may get tighter or clench yer teeth and eyes roll to the back of yer head for that split second. well that is our symphatic nerves reacting to the "pleasure."
i hope this was helpful..