Ultrasonic vocalizations (USVs) in rats are thought to contain ecological signals reflecting emotional states. These USVs are centered on 50-kHz. and frequency modulation (FM) is hypothesized to indicate positive emotion; however. results from recent studies are inconsistent with this hypothesis. https://www.alarecre.com/Disney-The-Nightmare-Before-Christmas-Lock-Shock-and-Barrel-Art-AirPods-Pro-2nd-Gen-Skin-p101716/