Apologies for the belated reply, but thank you to everyone who responded, for the tips as well as the reassurances. I definitely posted when my frustration level was at a peak (and it probably showed, haha), but I recognize that there's no reason to freak out or anything, since Iggy's still gaining weight at a steady rate, shedding well, and just overall behaving normally. I think next time I will try the trick of giving the rat's head a brief dip in hot water before offering. Not sure if he'd tolerate me reaching in to re-orient the rat for him without getting scared off, but I'm certainly not averse to trying that either, if it comes down to it.

Teenage rebellion, indeed!