This is a tool-assisted speedrun. For more information, see http://tasvideos.org/3919M.html. TAS originally published on 2019-03-12.
The Rat was released for Commodore 64 in 1984. The game was developed by Cymbal Software, Inc. and published by Personal Software Services.
The Rat is a top-view single-screen game where you are a rat spending the night in a cheese warehouse to eat all the cheese on various floors. On each floor there are six cheeses with letters spelling THE RAT and all have to be eaten to open the entrance to the next floor.
See the author's comments (http://tasvideos.org/6280S.html) for more information about the game and its mechanics.