Animals have evolved some interesting defense mechanisms and metabolic pathways. From the claws of the platypus to the diet of a fly, add your contributions!
Here's one to start off:
About spiders' eyes:
"Jumping spiders' visual acuity exceeds by a factor of ten that of dragonflies, which have by far the best vision among insects; in fact the human eye is only about five times sharper than a jumping spider's. They achieve this by a telephoto-like series of lenses, a four-layer retina and the ability to swivel their eyes and integrate images from different stages in the scan. The downside is that the scanning and integrating processes are relatively slow."