The Venomous Tentacula juice is juice extracted from a Venomous Tentacula plant. It acts like a poison. This "poison" is not deadly but, when consumed creates the sensation of burning on the insides. Also, the skin of the person who consumes it becomes a darker tone, usually purple.
Derwent Shimpling probably consumed a large amount of this substance, and his skin colour has become permanently purple.
Behind the scenes
- In Harry Potter Trading Card Game, the name of this substance is misspelt Venomous Tentacular Juice.