Witchcraft, obvs.
There are lots of these optical illusions. My partner who is an optician explained how they work but I can't recall now.
View attachment 434325
View attachment 434326
Title edited.Not wanting to come across all snowflake like but it may be worth putting a spoiler alert in the title - As a someone with epilepsy this properly messes with my head ... Wouldn't want any one triggering a seizure.
Interesting idea though, its a shame I cannot look at it !
It moves for me.