From reading this thread I'm grateful for (Eastern) Washington's mellow rattlers - I have stepped over more rattlers than anything. I think that comes from being exothermic, I tend to hike in cooler hours and snakes aren't out and about yet, but even on a hot afternoon I don't find rattlers to be scary.

Except around kids and animals. If a dog isn't raised to be cautious around rattlers, they risk getting bit on an encounter. I've heard too many sad stories about favorite companions either dead or suffering along a trail because the dog wasn't on a leash, approached a rattler too aggressively, and was bit.

I've never encountered a cottonmouth and don't want to - my trips to Florida are quick and don't typically allows for snake and reptile encounters. shudder