dull, stupid, suspicious
怚 centers on a slow, dull mental state: being stupid or sluggish in thought. The suspicious sense is a less common extension, perhaps from a dull person's mistrust.
怚 combines the heart radical 忄 with 且, which may have contributed a phonetic element. The exact historical development is uncertain, and the character is rare.
The heart radical 忄 beside 且 suggests a heart that is as dull and slow as a crude shelf. Picture a sluggish heart making the mind stupid and suspicious.
For ショ, imagine a dull person staring blankly at a show: show -> ショ, but their slow mind can't follow the plot.