There's a scientifically superior way to enjoy milk and Oreos.
Whatever your Oreo flavor of choice is—be it classic, Blueberry Pie, Swedish Fish, Jelly Donut, Fireworks, Mississippi Mud Pie, or any of Oreo's other many flavors—it's probably going to be more fun to eat when you dunk it in a glass of milk. Of course, if you've ever over-dunked a cookie, you might be hesitant. A cookie can easily go from delicious to gross with just a couple seconds too many sitting in milk. Now, thanks to the efforts of Lucas Reilly at Mental Floss, we know that the ideal dunk lasts about three seconds (and never more than four seconds).
Based on a study by Utah State University's splash lab, we've got a fair amount of information on Oreos' milk absorption. It turns out that, after just one second, your Oreo has already absorbed 50% of the liquid it's capable of absorbing. So, if you want to retain a fair amount of crisp, one second is probably your optimal dunk time. By two seconds, the Oreo was 80% of the way there, and it stayed at 80% for the third second. By four seconds, the Oreo had absorbed all it was ever going to absorb, so there's really no reason to dunk any longer than that, especially given that an Oreo dunked for four seconds is already super soggy (unless you want your cookie to fall apart).
One possible hitch: milk isn't just pure liquid. If the milk has more fat (a solid) in it, it absorbs slower. In fact, even the fat in the cookie can slow milk absorption. So, if you're dunking in whole milk, you're going to want to hold for a little longer than if you're dunking in skim milk. If you want to learn some of the physics behind it, including how capillary action and water activity affect the milk absorption, read Reilly's full and thorough explanation here.
[h/t Mental Floss]