Urthwurm

Urthwurms move differently from earthworms; rather than burrowing through dirt, they seek existing tunnels and are stopped dead in their tracks if they run into an obstacle head-on. But as invertebrates, their simple central nervous system makes them difficult to control, and the player's urthwurm's movements are directed with a single button that adjusts their trajectory through 10 levels of endlessly side-scrolling horizontal tunnel, carelessly littered with blocks strewn across its course. When the button is depressed, the wurm gets a buzz and adjusts its course to counter its downward motion and start heading up; when the button is released, gravity resumes its normal pull -- maintaining a constant course is hence very tricky and the player is much more likely to leave a trail looking something like a sine wave.

In short, this game is a re-make of the Palm classic SFCave.