A snail relentlessly follows your cursor.
There's a fun hypothetical that asks if you would accept the following conditions: you get ten million dollars, but a snail follows you for the rest of your life, and if it ever touches you, then you die.
Naturally, I took this hypothetical and made it into a chrome extension (the "snail that follows your cursor" part, not the "getting ten million dollars" part, though you are free to pretend this is the case).
Once you press the "start" button on the extension's popup page, a snail (shoutout Slay the Spire) will invisibly start tracking your cursor's position. It moves very slowly, but it is always moving. If it touches you, then you die (get a blue screen of death popup).
Probably quite susceptible to various glitches and errors. If you find any please reach out to firstname.lastname@example.org