In Super Meat Boy (Team Meat, 2010), a wall jump is two inputs: push away from the wall and press jump. In the first version of the controls, doing both at the same moment let go of the wall first, and Meat Boy just fell straight down. Tommy Refenes, who programmed the game, has said that was frustrating for him and for other players.

The fix: pushing away doesn't take him off the wall at once. He stays stuck for 200 milliseconds, and a jump pressed inside that window still counts as a wall jump. In Refenes's words, long enough that it feels right, short enough that you're never stuck on the wall. He wrote that every rule in the controls is set by how it feels when he plays, not by physics: "there are no formulas... it's just a big huge hack."

The shaft, the discs, the runner, the replay of 12 tries and the knob panel in this film are our own simplified version, built in code; the 200 ms is the game's own.

Which game's controls should we cut open next?

Sources: Tommy Refenes, blog post on Super Meat Boy's controls (Gamasutra, 28 Sep 2013); Refenes interviewed by Casey Muratori at HandmadeCon 2015; Refenes, "The Marriage of Level Design and Controls" (Full Indie talk); Team Meat, "Postmortem: Team Meat's Super Meat Boy" (Game Developer, 14 Apr 2011).
Not an official Super Meat Boy video. Not affiliated with Team Meat.
Sounds and music: our own, made in code.