The most intuitive and popular explanation for a high-demand price dip is that retailers are selling “loss leaders.” Stores advertise very low prices — sometimes even lower than they paid their wholesalers — for big-ticket, attention-grabbing products in order to get people in the door, in the hope that they buy lots of other stuff. You might get your turkey for a song, but then you also buy potatoes, cranberries and pies at the same supermarket — all at regular (or higher) markups. Likewise, Target offers a big discount on select TVs on Friday, which will ideally entice shoppers to come in and buy clothes, gifts and other Christmas knickknacks on that frenzy-fueled trip.

That is the supply-side explanation of what’s going on. But plenty of economists disagree, and argue that it’s actually demand-side forces — changing consumer preferences — that drive these price drops.

Consumers might get more price-sensitive during periods of peak demand and do more comparison-shopping, so stores have to drop their prices if they want to capture sales. Perhaps, during the holidays, the composition of consumers changes; maybe only rich people or people who really love turkey buy it in July, but just about everybody — including lower-income, price sensitive shoppers — buys it in November. Or maybe everyone becomes more price-sensitive in November because they’re cooking for a lot of other people, not just their nuclear families.

“People are a little less picky about what they’re buying for other people,” explains Judith Chevalier, an economics professor at the Yale School of Management. “Let’s say I prefer Coke over Pepsi. If I’m buying for myself, I’ll probably buy Coke even if it’s more expensive. But if I’m buying soda for a party, I have no reason to think everyone else also prefers Coke, so I’ll go with whichever brand is cheaper.”

One paper looking at canned-tuna prices argued that this kind of brand substitution was the primary case for an overall decline in price during Lent. It turns out that the cheapest tuna brands aren’t significantly discounted during Lent, but because the cheap brands temporarily accounted for a much higher share of overall sales, they dragged down the average price of a can of tuna.