It’s one of those ambiguity things of which this is the canonical example.
It’s also similar to this image:
https://i.pinimg.com/736x/60/16/5b/60165bfd56829bb95563a36cd69a5825--art-optical-optical-illusions.jpg
It’s difficult to see it as anything until it “snaps” and then it’s impossible to not see it.
It’s one of those ambiguity things of which this is the canonical example.
It’s also similar to this image:
https://i.pinimg.com/736x/60/16/5b/60165bfd56829bb95563a36cd69a5825--art-optical-optical-illusions.jpg
It’s difficult to see it as anything until it “snaps” and then it’s impossible to not see it.