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A pose where the top half of the body is stuck in the ground or water upside-down, with only the legs sticking out on top.
The name comes from Inugami-ke no Ichizoku (lit. The Inugami Clan), a 1951 detective novel written by Yokomizo Seishi. In it, there is a scene where a dead body is found in a frozen lake with its legs sticking out from the lake's surface. In the 1976 movie adaptation The Inugami Family, the body is found in an unfrozen lake, with the legs sticking out from the rippling waters.
This pose is tagged as "犬神家の一族" on Pixiv, regardless of whether or not it is a direct reference to Inugami-ke no Ichizoku.