When I caught on

Hello,

Dr. Szymanski has used his own perfectionism wisely. He does have 23 clean white canvas binders in his office that are arrayed like soldiers on a shelf, but he can see beyond them (and tell you what is in every single one). He does well in his career, has accrued multiple degrees and impressive positions, and as a bonus, has an awfully tidy house filled with a few choice midcentury items he has picked for their purity of line and arranged in symmetrical patterns. But his friends still tease him. “If you come to my house, everything is always in the same place,” he said. “And I have a friend who used to play a game when I’d have dinner parties. When I walked out of the room, he would move something, and the idea was everyone would wait to see how long it took me to move it back. When I caught on, he got more and more outrageous, until one morning I went to take a shower and found my bathtub full of pots and pans.”
(from NYT: No Room for Mistakes,Design Perfectionists at Home. Published in Published: January 25, 2012)
http://www.nytimes.com/2012/01/26/garden/design-perfectionists-at-home.html?pagewanted=3&ref=design

Can you please explain to me the meaning of "caught on"?

Takayuki
Thank you.