Supermarket selling seasonal items below cost? In a British supermarket, I saw the prices of Christmas chocolate gift boxes being cut dramatically (£1.50 to £0.15, and £7.50 to £0.22). I don't quite understand this behaviour, where the chocolate boxes are sold (presumably) below cost.
I've learned that this sort of strategy could be used to eliminate competitors and strengthen monopoly, but I don't think that's quite relevant for this case. It seems more of a clearance to me. What is the motivation behind such behaviour? Why don't the supermarkets just continue selling them at a low price, but not so low? Is it simply for saving warehouse costs?
Is it simply for saving warehouse costs?

Probably yes, holding onto inventory is very expensive. You have to pay for warehousing of the good, it takes the spot of some other inventory that might be in high demand. Food is also perishable so it cannot be stored indefinitely.
Stores have to always guess what demand for their products will be, sometimes they get it wrong and order excess inventory. It can often be more profitable to sell excess inventory below the production cost or many times even just to throw it away to make space for new products. Holding onto it would be a sunk-cost fallacy. The costs are already incurred in the past, even if they were a result of a mistake it does not make sense to try to double down on the mistake and hold onto them. It is more profitable to ignore the sunk-costs of getting them and make new decisions of what to do with the inventory based on new information.