Stepping Feet Illusion

Not having done any 2600 coding for a couple of years, I stumbled across a gif on Twitter of the Stepping Feet Illusion and immediately thought implementing it for the 2600 would be a nice gentle return to Batari.

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

It's an optical illusion produced by the contrasting bars - the blue and yellow "busses" appear to move out of sync with each other in a jerky stop/start motion such that their movement resembles alternating steps of feet but when the bars are removed it's clear that they are moving at the same speed.

https://youtu.be/-1wQeEu2uhE?si=UnOx9TK5gVe7sz6J