She left the little crab behind, seeing something in the sand that she wanted to investigate. What appeared to be a scrap of purple material was waving gently in the current, as if someone had dropped a handkerchief or thrown away the wrapper from a candy bar. Caddie, finding herself annoyed at the idea that someone would do such a thing, intended to pick it up, although it occurred to her as she reached that paper that she had nowhere to put it.

But it wasn’t waste. It was an animal. At least she thought it was an animal. It didn’t look like anything she’d ever seen. Perhaps half a foot in length, it had a soft purplish body from which extended what she could only think to describe as feathers, although really they were more like flags, flaps of pale pink that covered the creature’s back and fluttered as if a breeze were blowing them. It was unlike anything she’d ever seen, and she hadn’t the faintest clue what it was. It looks like something Stevie Nicks would wear as a shawl, she thought with amusement.

The creature moved slowly over the sand, doing what Caddie had no idea. She watched as it approached one of the flowerlike things she had seen earlier. With excruciating slowness it touched the thing’s stalk, sending it into retreat. Undeterred, the creature seemed to climb the stalk, its body sliding upward in a series of undulations. Then it stopped. When, a few moments later, the stalk opened and its owner emerged, the creature pounced, its head surrounding the head of its victim.

Caddie was enthralled. Clearly, the creature was eating. But what was it eating, and what was it itself? She had absolutely no frame of reference for understanding these things, and the complete mystery of them delighted her. When she saw Brian swim up beside her and point in the direction from which they’d come, she left the scene only with much reluctance.

The swim back was quicker, as if Brian was in a hurry to return to land. Caddie kept up with him until suddenly she felt herself rising quickly toward the surface. She fumbled with her inflator hose, trying to let some air out of her BC, but before she could even find the button she was at the surface. A moment later, Brian appeared beside her.

“What happened?” Caddie asked, finally finding the right button and releasing some air.

“You were too shallow to stay down,” said Brian. “You need to let air out as you get shallower.”

“How do I know I’m getting shallower?” asked Caddie.

Brian reached over and held up another of Caddie’s hoses, this one attached to a large gauge. “Look at your dive computer,” he said. “How much air do you have left?”

“I don’t know,” Caddie said. “Is that on there too?”