It is really interesting and amusing how persistent certain 'illusions' can be even when one is exposed to it just once and for a short time.

Fun story, this was a long time ago: I was interning at Google at that time. One day I tell my then cube neighbor about an interesting experiment on visual perception that I had read about. A professor at MIT had carried out experiments on his class. Students were asked to wear prismatic goggles that shifted their vision and then try to catch objects. Hilarity ensued, but soon enough the brain adapted to the shift. Same with inverting glasses, soon the students would not even realize that their vision was inverted. The fun part was when they took their glasses off, their motor reflexes would still compensate assuming that they were wearing those glasses. Much hilarity again. I was telling all this to my cube neighbor Michael Riley, not knowing who he was, he says with a twinkle in his eye "Yeah, that was us".

The most remarkable thing about these experiments that I learned from him was that the professor would provoke an illusion on the students on the first day of class. I dont remember exactly what the illusion was, but it was some visual artifact, seeing patterns that werent visible a moment ago, much like the OP. At the end of the semester the professor would demonstrate that the entire class could still see that illusion, although they have not been exposed to it in the intervening 4 months !

I tried hard to find an articles on these experiments and phenomena, but my google fu is not working today. I distinctly remember wikipedia articles on it, but am not able to retrieve them. Either my keyword memory has gone down or Google's search quality/relevance.

Navigating Google was such a nerd minefield, but in the best possible way. The excited student that I was, I ended up lecturing about longest common subsequence to Thomas Szymanski not knowing his association with the history of diff on unix. Same thing happened with SVM's, I was explaining its merits and demerits to Corinna Cortes, my other cube neighbor, not knowing she was the first author of the paper on SVMs. Not only would they not take offence they would all keep indulging. Then one day I step out for a break, a senior person whom I knew had a cube on the row behind me, approaches me, apologizing profusely and ad infinitum that he had got locked out, could I please let him in. No big deal, but he just would not stop apologizing and thanking me. A few days later a co-intern asks me if I know that guy. I said sure, I let him in once. He says no, do you know who he is. He asked me to checkout the name tag on his cube. I saunter off, "Brian Kernighan" !

An important takeaway of this internship was to experience the humility of all these people, and the sense that you are surrounded by such iconic stalwarts in CS and you wouldn't even know it because they are so... normal.

Coming back to illusions, another visual/auditory one that does not stop working even when you know exactly what is going on is the McGurk effect https://www.youtube.com/watch?v=G-lN8vWm3m0

EDIT Ummm so many downvotes ? I did not see that coming, would greatly appreciate what you found downvote worthy. It is always insightful to know how ones comment may rub someone the wrong way. Feel free to reply, I promise no offence will be taken and I will learn something along the way.

@tbirdz thanks for the perspective, I did not realize that it could come off as bragging. IMO you can brag only about things that you have achieved using your own efforts. For me it was a mix of foot in the mouth and an important learning experience, especially in humility.