Bava Kama 46a: If a cow gored an ox, and we find its newborn calf next to it, and we don’t know whether the calf was born before the goring or afterward, he collects half the damages from the cow or a quarter of the damages from the calf.
ב”ק מו ע”א וכן פרה שנגחה את השור ונמצא ולדה בצדה, ואין ידוע אם עד שלא נגחה ילדה אם משנגחה ילדה ־ משתלם חצי נזק מן הפרה ורביע נזק מן הולד.
When R’ Yaakov Kamenetsky was 10 years old, he had a rebbe who taught this Mishnah incorrectly. The Mishnah actually means that the owner of the ox is claiming that the cow was still pregnant when it gored. Since damage payments for an animal that was not accustomed to gore (תם) are limited to the value of the animal, he claims that the baby was inside its mother at the time of the incident, so that he may collect from both the mother and the baby. The owner of the cow claims that the baby was already born before the incident, and thus is not subject to collection.
This rebbe, however, got the arguments reversed. He said that the owner of the ox claims that the baby was already born, and it too participated in the goring, so it is subject to collection; the owner of the cow claims it was not born yet and is thus innocent.
Reb Yaakov, having grown up on his grandfather’s farm, had seen newborn calves and knew that they could hardly stand on their feet and are incapable of goring. He asked his rebbe, “But how could a newborn calf gore?” The rebbe shouted at him, “How dare you argue on a Mishnah like an apikorus? From asking such questions, I am sure you will someday go off the derech!”
The young boy humbly accepted his rebbe’s explanation, but still struggled to imagine a baby calf causing damage. But then he remembered hearing his mother read a story from the Tzenah Urenah (Parshas Noach), based on a Midrash (Vayikra Rabbah 5:1) which says:
עובדא הוה בחד אתתא דילידת בלילה ואמרה לברה אזיל ואדליק לי בוצינא ואנא קטע שורך אזל למדלק בוצינא ופגע ליה שידא שריהון דרוחתא עם דמתעסקין דין עם דין קרא תרנגולא א״ל אזיל גלוג לאמך ואמור לה אילולי דקרא תרנגולא הוינא קטיל בך א״ל אזיל גלוג לאמא דאמך דלא קטעת אמי שורי דאי קטעת אמי שורי הוינא קטיל לך.
Before the Mabul, a mother once told her newborn baby to go fetch a candle so that she could cut his umbilical cord. While out, he met the Prince of the Demons. As they were talking, the rooster crowed. The demon said, “Go tell you mother that had the rooster not crowed, I would have killed you.” The baby replied, “Go tell your mother’s mother that had my mother cut my umbilical cord, I would have killed you.”
The young Reb Yaakov concluded that the Mishnah must be talking about a monetary dispute in the generation before the Mabul, when even newborn babies were strong and capable. Later in life, he joked, “This was the first of my chiddushei Torah.”
Source: Making of a Godol, p. 144