When you nail an exam, you really do well on it. When you hit the nail on the head, you get something exactly right. That snake really got you!
A blow torch is used in a construction job or some other job. It is a device you hold in your hand...it might look a little like a spray gun; a flame shoots out of it when you press the "trigger" and you use the flame to burn something off or for some other purpose.
In other words, when the snake bit you so effectively it felt like something burning! Not very much fun!