I bet they stopped lined up north-south. I expect that this effect is due to the earth's magnetic field. They are trying to be a compass, but keep overshooting because of the strength with which they are drawn north south. Is there an engineer in the house?

I think it's more likely they're simply spinning because they came at each other fast, and from the side.

it's far more to do with inertia than anything. you can buy some very strong "tweeting" magnets from the gas station impulse-buy section for like $2.00. it's the same concept, but because of the shape, they don't continue to spin for that long. they're oval shaped and see-saw back and forth on one another causing the tweeting sound.

They spin so fast because of conservation of angular momentum. They start out far away with a lot of angular momentum which they conserve when getting closer by starting to move faster. It's the same as when ice skaters pull their limbs in to start spinning faster and then extend them to slow down.