>>71034781The carpet going over the corner of the stairs creates a bend in the carpet, which allows for the protruding carpet fibers to move more along the direction of that bend, since they aren't in contact with, and propped up by, the surrounding fibers. It's like when you cube up a mango - those cubes are much more wigglable once you push the skin inward.
This allows your foot to have more possibly of movement in a position that you would normally consider stationary and stable in that moment of that particular step. Adding socks into the mix ups the slipperiness, since they both increase the layers of unfixed material between flesh and stair and decrease the friction between those materials.
