Some cats like to steal their master's socks and then carry them around in their mouths. There are various reasons behind this unusual behavior, but also instinct.
The behavior is instinctive and not learned - for example from a dog as a roommate. For all cat owners with missing socks, it's worth taking a look at their cat's basket or favorite hiding place - because the washing machine isn't always the culprit. You can find even more exciting animal topics in the free partner newsletter from Landtiere.de, which you can subscribe to right here.