https://e621.net/posts/2396474?q=zero-sum
https://static1.e621.net/data/89/a7/89a760b6fbc6213bee4da4da6cfda365.webm
https://static1.e621.net/data/27/43/2743ec5e9e25cc895d9ee7af3f01be41.webm
https://static1.e621.net/data/91/08/910872736f3ea9702735c9b01e2971e8.webm
https://static1.e621.net/data/9c/72/9c72782fcc2768b89561880775244ab1.webm