[MegaDeKay]

And you'd have to pop the ball out every now and then to clean the crud that had built up on the x & y rollers that otherwise made the on-screen pointer stick and skip. Good times.

[hyperdimension]

And even though we're well into the future of optical mice, when my Bluetooth mouse disconnects for a few seconds, the habit of thunking it on the desk a couple times persists... (to unstick the ball)

[dhosek]

Then there were the first-gen optical mice which required special mousepads with a grid on them for the mouse to know how it was being moved.