While I would say that even an experienced person might think that was a blacktail (or timber) rattlesnake.....if they only took a quick glance at the photo...it's clearly a diamondback watersnake. An especially pretty one at that...

While I don't have the claimed experience of the expert in question, I do have a blacktail rattlesnake (and a timber) and when I can't tell the difference between a rattlesnake and a watersnake, it will be time to hang up my hooks...
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What goes up must come down...unless it exceeds escape velocity.