Re: How friggin awesome is evolution!
It can't be evolution - if the poison kills you, then you can't breed in a protection against it, therefore this is 100% proof that evolution does not exist.
I should think that how this evolves is something like this.
To start with, the mice attacked scorpions the same way mongooses attack cobras. Very carefully. They're faster and smarter than their prey, so mostly they get to eat it rather than die. The less nimble ones get dead more often, and the species gets nimbler. Note that all hot-blooded species have a fundamental advantage over cold-blooded ones in the morning, before the cold-blooded ones have a chance to re-warm their bodies from the overnight chill.
Sometimes when battling or eating the prey, a small amount of venom gets into their bloodstream. Enough to harm but be survivable. Genetic variability means that for the higher doses, some survive and some don't. Gradually, genetic tolerance of the venom gets bred in. When a sting ceases to be lethal 100% of the time, risk-taking mice gain an evolutionary advantage over the original extremely risk-averse mice.
And so by slow and gradual evolution, you arrive at mice that laugh at scorpion venom.
I'd guess that the final stage is that mice which feel less pain when stung have a slight advantage over ones which do. Pain is distracting, so they more often get caught by larger predators if they suffer pain? That would create an evolutionary bias in favour of "hard" mice.
One other thing: ability to acquire tolerance of venoms by an individual is near-universal in mammals, including humans. It's the standard immune system response. The immune activity degrades a foreign protein before it can fatally degrade the host's proteins, and is then primed to mount the same response faster and better next time. Immune responses are passed (or primed) from mother to child via breast-milk. It's an area we don't yet fully understand. There may be epigenetic factors at work, and Lamarkian evolution may not be completely discredited when it comes to inherited immune response. Just a thought.