"An apple of discord is a reference to the Golden Apple of Discord which, according to Greek mythology, the goddess Eris said that she would give "to the fairest" at the wedding of Peleus and Thetis, sparking a vanity-fueled dispute between Hera, Athena and Aphrodite that eventually led to the Trojan War...Thus, "apple of discord" became a euphemism for the core, kernel, or crux of an argument, or for a small matter that could lead to a bigger dispute. "