Final answer:
Psyche releases a deadly slumber from the jar given by Proserpine when she unseals it, which is emblematic of the dangers of violating prohibitions in mythological tales.
Step-by-step explanation:
When Psyche unseals the jar that Proserpine (another name for Persephone) has filled for her in the Underworld, instead of finding a beauty charm, a deadly slumber comes out. This motif of forbidden opening of containers brings forth disastrous consequences and is a common element in mythological narrative.
By opening the jar, Psyche succumbs to the slumber, which prevents her from completing her task and puts her in further peril, only to be rescued later by Cupid.