the biggest mystery

So I was finishing up laundry, and yet again, I came up with several lone single socks. And they always seem to be Dav's black socks. I'm a stickler for pairing up socks so they are together in the sock drawer. I mean, we have 2 feet so organizing this much makes sense to me. When I first moved in with Dav, all his socks were haphazardly piled in a drawer. So one day, I sifted through all of them, found the pairs, and decided to use the singletons for rags. But I keep finding more, and today I ended up with 3 more! I do all the laundry (remember, I like this activity) and just don't get how this happens. I double checked with the 'rag' socks and sure enough, NONE of these match! Any ideas??