End of life twitching

After a good shot to the head, most of the rabbits I have been taking have the end of the life twitch. I understand it. I'm used to it.

But the other night I had an end of life squeek/yell/vocal. 

I put a clean shot from my Veteran .22 right through it's forhead, down the length of it's body. A shot that dropped it in place. But when I went to retrieve it, it was not only twitching, but it was still squeeking at me. I was too close to my neighbor's house to take an up close shot, so I hit it with a hammer I had nearby (I know, not pretty, but I wanted to end it quickly). Still noisy. I grabbed it's hind legs and did a quick flip and smacked it into the pavement thinking I would crush it's skull and spine...STILL made noise. I carried it into my yard and used my P16 and put a .177 point blank into the side of it's head...STILL noisy! It was another shot that finally silenced it.

Someone tell me that they've experienced something like this and that I wasn't just making a horribly inhumane kill. Or did I just find a freak of an animal that just wouldn't go down.
 
thats pretty brutal man lol .. yeah i was after a squirrel one time and i was pissed atm and gut shot it only shot i had, then proceeded to hit it with the rest of the clip and finally knocked it out of the tree, and it was running past me dragging guts makin all kinds of racket but i was empty .. so proceeded after it clubbing it with the but end of the gun . yeah i didnt feel good about that one at all, broke my stock to lol .. i felt so evil, try not to let things like that happen now ...
 
My best guess would be that the pellet did not scramble the brain. Most often, a good solid fart will kill a rabbit.

To remedy that unfortunate outcome (non-insta-death) - you can quietly and discreetly step on the head. It will pop like a ping-pong ball under the average man's weight on one foot. A little hop may be needed if your shoes or the ground is soft. 
 
When I was a boy my uncles took me hunting. One of them could flick a rabbet while holding it's head and the head would come off. I tried it and it didn't work for me. Rabbet was still a little bit alive and obviously did not appreciate my lack of skill. Every time I tried the rabbit just came out from between my fingers and went flying. I finally stepped on it's head and tugged on it's legs - worked - head came off.

I shot the top of the head off a dove this year and it wasn't making noise but was still looking at me and flipping it's wings some so it got one in the chest.