Arrows to steer. Eat the thing, get longer, do not run into yourself or the wall. Score in the corner, and a restart button for when it goes wrong, which happens the first time at about forty seconds.
There is no menu, no difficulty and no skin. It exists because the game does not need any of that, and it is here for the particular occasion where you want to play something for four minutes with no decisions in front of it. The whole thing is smaller than the average web page's stylesheet.