How come some cereals make a popping sound when you pour on milk? And why do we get white spots on our fingernails? asks Karen Perez, via email.

While Rice Krispies may be the noisiest cereal, other puffed cereals may also snap, crackle and pop when doused with ice-cold milk. Just as corn is popped into popcorn, rice, wheat, and other grains can be puffed up into fluffier versions of themselves. In the case of puffed rice, cereal makers oven-toast the rice, which has been conditioned with water. As the water turns to steam, rice kernels puff out like microwaved popcorn.

Unlike the compact, hard walls of an uncooked rice kernel, the walls of puffed rice are stretched very thin, making each kernel quite fragile. When cold milk is poured on, the shock causes the walls to crack like a thin glass crystal. As the milk is (unevenly) absorbed by the puffed rice grains, the snapping, crackling and popping sounds come from the fracturing of the walls and the escape of air bubbles trapped inside the kernels.

Meanwhile, if you pick up your spoon to eat your talking cereal and notice a few white spots on your fingernails, don’t panic. Some cultures see the white spots as a good luck sign, and even call them fortune or gift spots. There’s also the old idea that someone with a white spot on a fingernail is in love, or that the number of white spots equals the number of “sweethearts” a girl has. In an Alice Hoffman novel, a white spot appeared on a character’s fingernail each time he lied, a telltale sign like Pinocchio’s growing nose.

But fibbing, falling in love, or winning the lottery actually have nothing to do with white spots, unless you happen to hit one of your fingers in all the excitement. Dermatologists (skin doctors) say that white spots and smeary streaks happen to all of us, and are usually nothing to worry about.

The official name for white nail spots is the somewhat scary-sounding punctate leukonychia. (In total leukonychia, the entire nail turns white.) Kids and adults often have one or more random white dots or marks on their nails, especially if they are hard on their hands. Dermatologists say the spots appear because of repeated dings to the nail bed at the base of a fingernail (say, by a striking ball when playing sports). Much rarer causes include infections, systemic illnesses and dietary deficiencies.

White spots are a mix of keratin (a tough protein) and air. The spots are places where, due to an minor injury to the nail bed, new nail cells were incompletely formed or “keratinized.” The white spots will rise higher as the nail is pushed up by new growth from the nail bed. Since a nail grows about one millimeter in 10 days, it can take months for the spotted part to reach the tip for trimming off. Meanwhile, you can look at your nail spots and relive memories of all the insults and injuries to your fingers in the past year.