Just keep a few sizes of frozen rats on hand and make sure they get at least one of those and it will prove that they are not "hooked" on asfs. All mine take asf or rats. Live and f/t no problem. I think it is less about imprinting and more about the fact that ball pythons can just suddenly decide they only want a certain kind of food..and then later decide that they don't really care what they eat. Their habits change. Steering clear of asfs isn't going to save you from the ever picky ball python.
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