Our parsha teaches us that Kohanim may eat sacred things (e.g., Teruma) only in a state of purity. Try to solve the following riddle related to the laws of tummah and tahara.
Reuven did something, and something that was tammeh became tahor, while something else that was kosher became pasul.
What did Reuven do?
Answer (from page 1): Reuven immersed a tammeh vessel in a mikva that had exactly 40 se’ah of water. When he took the vessel out of water, the vessel naturally had some mikva water on it, making the volume of water in the mikva less than 40 se’ah. Hence, the vessel went from the state of tummah to the state of tahara, while the mikva turned from being kosher to being pasul.