This is going to run a little contrary to what others have said and it comes from experience with my collection and interactions with wild snakes throughout the continental US. First, the only aggressive snakes I have ever encountered are cotton mouths. This is the only snake that I have ever interacted with that will come at you even if it has the chance to escape. Even big rattlers will leave you alone if you do not threaten them. Ball pythons are the shyest snakes I have ever dealt with. Not one that I have encountered would I ever classify as aggressive. If pressed, there is the relatively rare animal that will strike defensively. Babies on a little higher percentage, but they usually grow out of it. I have two adults in my collection, that were purchased as adults that are super high strung. Both are pastel morphs. These guys will strike if startled. I think I have them beyond the "that giant thing is going to eat me stage" however I have to be careful. I am working with these animals every day at this point. Things are slowly getting better. I like the challenge because most of my animals are super mellow. Now back to the original question. If I go more than a few days without working with these animals I am back to ground zero and have to start all over again.
All that said, mellow animals almost always stay that way. If there is a sudden change in temperament it is usually caused by something.
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