For mischievous young sealions, the ocean is a giant playground. Lying on the sandy seabed in the cold, azure waters of the Galapagos Islands, I'm suddenly aware of a large, shadowy form to my left. Before I have time to turn around it races away. Moments later, a big-eyed, whiskered face appears less than an arm's length away. It's a young sealion, hovering effortlessly upside down in front of me, deliberately blowing bubbles into my mask. But as quickly as it appeared, the super-sleek, brown-coloured sprite is gone. Now something starts tugging my fin - and it's not my dive buddy. Craning my neck awkwardly (how very un-sealion-like), I glance backwards to find my lithe new friend nibbling on my flipper. It then surges off to the side, picks up a small rock in its mouth, and tosses it upwards in a solo game of catch. After a few more rounds of rock-toss, it shoots off, presumably to look for a more exciting playmate.