be insane, severe, violence
猖 centers on extreme, uncontrolled behavior: madness, violence, or severity that goes beyond normal limits.
猖 combines 犭 (animal) with 昌, which likely contributes the sound. The animal radical suggests wild, untamed behavior, fitting the meanings of madness and violence.
A wild animal 犭 beside the bright sun 昌: imagine a beast driven mad by the heat, becoming violent and severe.
For ショウ, picture a show of insane violence: a wild animal on stage under bright lights. Show -> ショウ.