'Horns'

When disturbed, Black Swallowtail caterpillars(and other Swallowtails as well) show their 'horns. I sometimes like to 'tickle' the cats to encourage them to display their bright orange osmeteruim (osmeteria, plural). It's an eversible horn-like organ located just behind their heads, likely used to ward off predators. It reminds me of the forked tongue of a snake. It's withdrawn as soon as the perceived threat is over, leaving a nasty oder. Pretty cool, right?