Buffalo Lake NWR today, southwest Randall County. Wife almost stepped on this little guy, who was probably 8-10" long. He was doing the whole "I'm a rattlesnake" act, waving his head, and shaking his tail as if it had a rattle.
He was blocking a narrow gate, so when the photoshoot was over, wife stepped over him and placed her foot about 8" past him. He struck at her. Cracked us up. When I stepped, I intentionally stepped close, and he struck at me, too.
Behavior seems like a bull snake, but I've never seen one this color. Google looks at the image and calls it a green whip snake, which lives in Europe.
Any ideas?

Facebook video, sorry, but it shows the tail shake
https://www.facebook.com/576047767/videos/pcb.10162510067972768/1029301982513201EDIT: What about a speckled kingsnake?
https://www.inaturalist.org/guide_taxa/850015Quote:
NOT venomous. Head and neck appear to be the same size as the body,smooth scales, round pupils. Uniformly cylindrical body is black with yellow to white spots on each scale. Belly is yellow checkered with dark blotches. Typically 3 to 4 feet (91 to 120cm) in length. (J. R. Dixon and J. E. Werler, Texas Snakes: A Field Guide, University of Texas Press, 2000.)
Behavior
When threatened, the speckled kingsnake will shake its tail like a rattlesnake to deter predators. It frequently will expel musk and feces or bite when threatened.