Here’s another version of the illusion I’ve been working on with my colleague Priscilla Heard. The bright V shaped zones imposed on the faces look like they are expanding or contracting sideways, especially near the sharp end of the Vs at the bottom. It can be hard to see that it’s an illusion, because the faces really are expanding. But to the right an isolated bright zone shows that objectively the V tracks are quite static. You may still see a bit of illusory lateral expansion even in this isolated set of tracks, but note that the top right corner of the track is quite static in relation to the corner of the movie.