No, head to the cave

Never one to turn down the opportunity to explore, the Doctor shot off in the direction of the cave with Rose following on behind.

As they approached the cave, they could hear the sound of trickling water. A spring trickled from the mouth of the cave into the sea. The water looked clear and inviting.

Still feeling parched, Rose put her hand into the water and drank some of the cool refreshing water.

As the Doctor watched, he saw Rose's face begin to flush and saw her starting to run her hands over her body in a very provocative manner.

The Doctor realises there must have been something in the water.

But what?