<p><strong>The Gemara in Sanhedrin 100a tells a story of Rav Yochanan claiming that in the future, the gates of Yerushalayim will be massive pearls (30x30 Amos) that are hollowed out. When a student mocked this claim, he ended up seeing angels actually hollowing out such pearls. After Rav Yochanan criticized him for mocking Chachamim, he turned into a pile of bones. </p>