What happens to an engine during a cold start in sub-zero temperatures?

I had a '74 Triumph Spitfire with a 4 cyl and it came stock with a manual choke, as any proper auto should.

That car, to this day, remains the fastest starting vehicle I've ever owned or seen. Hot or cold (with a bit of choke) it would start seemingly with 1/64th of an engine revolution when you hit the starter. You couldn't bump the key so little that it wouldn't start. I never drove it in the Arctic Circle, but I bet it would start there too.