I collaborated with an animal science student, who needed a piece of communication responding to Orcas and Blue Whales in capitivity. Aimed at young children, I had an idea for a charity pack/activity, to be sold along seafronts up and down the UK.
The Blue Whales are made of litmus paper, and will only turn back to their rightful shade in seawater - not water from a tap, bath or bottle. The branding correlates with seawater's pH.
It's a simple device, gently illustrating how these animals function best in their natural habitat. The inside of the pack would have further information for the parents.