Holidays are approaching and it is time to stop thinking about serious physics and discuss some recreational physics. I will discuss the following problem, which was assigned in the very first International Physics Olympiad in 1967, a competition for high school students: "Consider two identical homogeneous balls, A and B, with the same initial temperatures. One of them is at rest on a horizontal plane, while the second one hangs on a thread. The same quantities of heat have been supplied to both balls. Are the final temperatures of the balls the same or not? Justify your answer. (All kinds of heat losses are negligible.)" This problem is now considered a classic and can be found in several problem books and collections. The main reason for its popularity is that the solution usually presented, while being tricky to find, is very simple and elegant, and uses tools accessible to a high-school student. Unfortunately, it turns out that this solution is actually wrong! I will discuss why, and derive the correct result. The audience is encouraged to think about the solution in advance!