A listener suggested this one (Thanks Dave).  Optical mouse.  I have no idea how it works. Do you know how it works?  Well, I gave myself 20 mins to go find out.  Now I'm sharing with you what I found out.  This is episode number 5.  Yes, you are allowed to subscribe.

https://en.wikipedia.org/wiki/Optical_mouse

https://www.explainthatstuff.com/computermouse.html

Music: Cheeky by Shane Ivers - https://www.silvermansound.com