I was bitten some years ago in Russia by Vipera berus and anyone who says it's no more than a bee sting, is very, very, wrong. The antivenom (Zagreb) is not always administered straight away as in itself, can have some unpleasant side effects. I was put on a drip and monitored for two hours before they deceided that my body was coping with the bite and that I didn't need the antivenom.
I was bitten at the first joint of my middle finger. I then had three weeks during which my entire hand and arm were so swollen, I couldn't hold them by my side as it was too painful. I can't imagine what a Rattlesnake or Pit Viper bite must be like.
For those that haven't seen the images.