Detective Conan - Season 1 Episode 434 : The Great Dog Coeur's Triumph

Conan and Ran pass by a dog park and befriend two couples whom each own a dogs; one is named Musashi and the other is named Coeur. Yoriko Nakatani, the neighbor of the owner of Musashi, the Tsutsumi couple, asks Kogoro to investigate the dog Musashi who acts aggressively to her. Conan and Ran disclose they believe she did something to upset the dog, causing her to leave. The next day, Nakatani's mother in law is seemingly killed by Musashi when his teeth marks are found on her throat.