Let's Play: TMNT - Tournament Fighters ~ SNES

[gamexmasterxfire]

The reason they left the hooker but not Aska's butt is because background animations are one large image that loops in the background, while sprites work by the game looking up a spritesheet from which to read animations. Then, spritesheets within the game can be altered more easily than any other animation, since altering a detail in the background requires to alter the whole thing, which in larger file than the sprites.