ball python prefers smaller prey items once a week?

I have a 2010 male normal that will be nine months old this month. He weighs 964 grams. He will only eat one small adult mouse for me once a week. I have tried offering two and he wants nothing to do with the second one. This boy used to eat small f/t rats and then he switched to live small rats. He has become very picky and will now only eat one live small adult mouse. He is growing very well, sheds perfectly, and never refuses a meal as long as it only one small adult mouse. What is going on here exactly? I am sooooooooo puzzled.

I recall reading that BPs tend towards picking a favorite food...maybe this is his. If he's still growing and acting fine it should be ok.

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