At the beginning of the movie My Neighbor Totoro , Mei and Satsuki saw an acorn for the first time inside the house.Then Satsuki is walking in a funny way to catch it. It seems she is walking on her knees, but why?
The floor of this room is made of tatami mats. In Japan, it is really important
to walk without sleepers or shoes on tatami mats. Bare foot or socks are ok. Or
in case you are in a rush and don't want to remove your shoes, you can do like
Satsuki and walk on your knees. It is a question of good manners and you
would not do that to someone else place.
Nowadays, a lot of houses or appartments have one (or more) tatami room(s). This is a traditionnal room with some restrictions (no shoes allowed, should not make the tatami mat dirty, etc.). Thus new appartments or new houses may have no tatami rooms (especially in big cities).
Japanese people make lot of effort to keep their homes clean. In every house there is an entrance (genkan) where people should remove their shoes. And usually, sleepers are provided to the guest. Walking with shoes inside an house is strictly prohibited.
People who have visited Japan probably remembered when they had to remove their shoes (and carry them in a plastic bag provided) to visit a temple, a shrine or a castle. It's a little bit disturbing to walk around with the shoes in a plastic bag but it keeps the facilities more clean.
There are other kind of sleepers that should be used only in the bathroom. The guest should leave his (or her) sleepers outside of the bathroom and use the "bathroom only sleepers" inside the bathroom.
On a famous TV show named Aibou (相棒) about cops investigating, we can see the cops wearing
sleepers when they are questioning a suspect in his house. Thing that we don't expect
Jack Bauer to do!
(unfortunately I couldn't find a screenshot of this show with the actors wearing sleepers)
Back to My Neighbor Totoro , we can now guess what Mei is doing on the image below with her leg:
She is trying to remove her shoes to go inside the house to pick up an acorn.