How do you tell if it's deadly. It didn't look like all the king snakes I have seen over the years in the garden, they are always pretty. Usually all black with a little yellow/green markings. Even the big ones are harmless. They just lie there or crawl off. But this snake acted like it was freaky friday or something or like I had a hoe in hand and death in the eye. It was long and fat and mostly a dusty black with some brown gray marking in the middle. It definitely had that arrow shaped head. I wouldn't call it offensive aggressive, but it was all defensive aggressive. It's head was raised at least a foot in the air and was waving around and it was working it's mouth funny like. And it was moving it's whole body in a sideways motion. Cottonmouth? I have seen some huge king snakes on the farm but this was the first truly scarie snake I have ever seen, including the copperheads. This was mean snake. I let it go, but man I'm nervous about the garden.