As best as I can figure out by immersing myself in a couple of books and within the depths of the Internet, I conclude that this is a picture of a cabbage looper, a caterpillar found on my mint plant this afternoon. After about twenty days, this caterpillar becomes the ni moth.
Moving fairly quickly and nimbly with a looping motion, it moved to the bush next to the mint, almost disappearing. In the meantime, I jumped into the house hastily to retrieve my camera.
Aside from the information and sources provided by Wikipedia, I found other sites of note, namely, the University of Florida's Entomology and Nematology site, in which they list the cabbage looper as a Featured Creature; and Butterflies and Moths of North America, a site with bottomless information and sources about these amazing creatures of God.