Each month in the modern Gregorian calendar consists of at least 28 days. That number would be a nicely rounded 30 were it not for February. While every month besides the second in the calendar contains at least 30 days, February falls short with 28 (and 29 on a leap year). So why is the most widely used calendar in the world so inconsistent in the lengths of its months? And why is February stuck with the fewest number of days? Blame it on Roman superstition.

The Gregorian calendar’s oldest ancestor, the first Roman calendar, had a glaring difference in structure from its later variants: it consisted of 10 months rather than 12. In order to fully sync the calendar with the lunar year, the Roman king Numa Pompilius added January and February to the original 10 months. The previous calendar had had 6 months of 30 days and 4 months of 31, for a total of 304 days. However, Numa wanted to avoid having even numbers in his calendar, as Roman superstition at the time held that even numbers were unlucky. He subtracted a day from each of the 30-day months to make them 29. The lunar year consists of 355 days (354.367 to be exact, but calling it 354 would have made the whole year unlucky!), which meant that he now had 56 days left to work with. In the end, at least 1 month out of the 12 needed to contain an even number of days. This is because of simple mathematical fact: the sum of any even amount (12 months) of odd numbers will always equal an even number—and he wanted the total to be odd. So Numa chose February, a month that would be host to Roman rituals honoring the dead, as the unlucky month to consist of 28 days.

Despite changes in the calendar as it was altered after Numa’s additions—alterations that include the shortening of February at certain intervals, the addition of a leap month, and eventually the modern leap day—February’s 28-day length has stuck.

Camels have long been known for their ability to go weeks at a time without needing to drink water—an ability that makes them particularly useful pack animals for people traveling across arid environments and that earned them the nickname “ships of the desert.” Camels are also known for their prominent humps (either one or two humps, depending on the species), which leads many people to believe that these are used to store water for access at a later time. However, camels’ humps actually store fatty tissue, not water, which is used as a source of nourishment when food is scarce.

So why do camels store fat in these humps instead of having it spread equally throughout their bodies, like other mammals? Camels typically live in the desert, where food sources can be hard to come by. When a camel is unable to access food for a long period of time, its body is able to metabolize the fat in the humps for nutrition. The humps can deflate and droop if the camel has gone a particularly long time without food, but they will sit upright again once the camel is able to refuel. The camel’s humps also help the animal regulate its body temperature, an important feature in the desert, where temperatures can be extremely high during the day and drop drastically at night. By concentrating fatty tissue in humps on their backs, camels are able to minimize heat insulation throughout the rest of their body during the day when the temperature is high, and their body temperature rises. Then, at night, the extra heat dissipates through the rest of the camel’s body so that their body temperature is not too low when the temperature is cooler.

Although the humps do not store water, camels are still incredibly efficient in the amount of water they use per day, which is why they are able to go nearly a week without drinking. This is partly due to the unique shape of their blood cells, which are oval. Oval-shaped blood cells allow camels to consume large amounts of water (up to 30 gallons in one sitting!) since the cells are more elastic and can change shape more easily. This shape also allows their blood to flow more easily when water is scarce, which is common in a desert.

A camel’s humps are incredibly important for the animal’s survival in a tough environment like a desert. Without its humps, a camel would be more likely to overheat and sweat—but it’s still the oval-shaped blood cells that help the camel retain so much water, not the humps.