That's one of the neatest illusions I've ever seen
Clue #1 : there is no green dot
Ever suspicious of things webbish, my first thought was that any second a huge terrifying face was going to jump out of the animation and scream at me. I even turned my speakers down waiting for it.
My second suspicion, after taking it in for a few seconds, was that the "green dot" had been cleverly faded into later frames...but no, it had only been cleverly faded into my perception.
Neato! I think the mysterious second effect is when the pinks dots disappear altogether.