During the program, he said, "In the past, I said my hobby is inventing new things. People responded with, 'aren't you just trying to look cool?'. But, at the time I actually was creating new inventions." To show that he wasn't lying, he brought a patent certificate for one of his inventions.
In addition to the certificate, he also brought a drawing of his work to explain to the cast of the show his invention. He was then asked if he had commercialized the creation but revealed his goal was to just receive a patent certificate thus decided not to do so.
Did you know Yunho had this kind of a hobby?