Hover flies are incredible. They hover, then zip off somewhere and come back to exactly the same spot as close as anyone has been able to measure. Talk about a GPS system!

I'm familiar with most of what was said in the eye thing. However, I didn't know trilobites had calcite lenses in their eyes. Calcite has two refractive indices. If you look through a clear piece of calcite at an object, you will see two objects, and they will move if you rotate the piece of calcite. I wonder how the trilobites used or adjusted for that characteristic.