This occurs after Thravum makes his saves
The sliding jelly collides with Florr after she tumbles over, luckily, her horse storm surge is missed.
Florr takes Acid Damage: 1d6 + 1 ⇒ (2) + 1 = 3 from making contact with the sea jelly. Your skin feels numb.
The sound of arcing electricity grows in volume and you see the sea jelly begin vibrating as it slides off Florr into a smoking vaporous puddle that begins quickly soaking into the ground, it's then you notice a small battered tin box that was apparently suspended in the jelly that had gone unnoticed.