I am on vacation in northern Chile and encountered an interesting staircase in one of our hotels. The uppermost step was a little higher than the others, causing the whole family to stumble almost every time we passed it on the way upwards. Similarly, we always got a few extra centimeters when walking down, making us almost fall over when starting the escalation.
This staircase reminded me about action programs, the anticipation of actions based on a perceived rhythm. In this case, the rhythmic nature of the steps of the staircase. Based on ecological knowledge about how staircases typically work, with equally displaced steps, one predicts the actions to climb the staircase. However, when this rhythm is broken, due to one step being slightly higher than the others, it breaks with our prediction. After almost stumbling several times, we began getting used to it, but it still felt weird each time.