Compare the stationary and spinning dot rings. Both sets of dots change color at exactly the same rate, but the moving ring may seem to change more slowly. Keep your eyes near the center and switch attention between both sides of this optical illusion.
Music: "Firesong" by Kevin MacLeod (incompetech.com), licensed CC BY 3.0 US. Excerpt trimmed to 30 seconds and mixed with this video.
Source: https://commons.wikimedia.org/wiki/File:Firesong_(MacLeod,_Kevin)_(ISRC_USUAN1100598).oga
License: https://creativecommons.org/licenses/by/3.0/us/deed.en