Explain Collider Bias with Simulated Data

I try to explain collider bias leading to selection bias with simulated data, based on an old but awfully bad joke we used to tell in school. There are way better places to learn about collider bias. See for example here the text mentioned in the video: https://www.hdruk.ac.uk/news/we-should-be-cautious-about-associations-of-patient-characteristics-with-covid-19-outcomes-that-are-identified-in-hospitalised-patients/ . Please also see this commentary on situations where there is selection bias without collider bias. https://academic.oup.com/aje/article/185/11/1048/3849417