Blake,
How often do you feed him? It is not good for a cornsnake to be fat. In fact, it can lead to alot of other health problems sooner or later. I have never really noticed aggression increasing with less frequent meals but maybe if you handle him more between meals he'll calm down a bit. I would slow down his feeding frequency (every 14 days?) and start weighing him with a digital scale (you can buy them everywhere...including the post office or staples or office max).
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Sincerely,
Jason
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I'm stopping at 60...I swear!