At first the Hoobs think the water in the Hoobypond might be boiling. But the water isn't even hot.

The Tiddlypeeps have soapy bubbles filled with air. So the Hoobs realise there must be air coming from somewhere in the Hoobypond.

Roma reports from a geyser. She explains that they're made when air rushes up from under the ground, pushing Hoobloads of water into the air. But the Hoobs realise that the Hoobmobile is under their pond and there's no air rushing up towards the roof.

There's a story about some fish that leave a trail of bubbles. But the Hoobs can't find any fish in their pond - only Groove's missing Hoobycup.

When Groove sees a Tiddlypeep putting a cup in a bowl of water, he realises that his Hoobycup is part of the answer - because it was full of air when it was in the pond!

You can help your child to find out about bubbles!