"You have no idea," the Doctor said. After a second, he added, in a more flippant tone, "No, wait, maybe you do. You've been me, before."

What was that creature? Why would it do that?

The Doctor sniffed, then nodded, keeping his eyes on the water. "A Time Lord only has thirteen lives. Losing one because I don't want to deal with the life I've led's a bit immature, don't you think? I'd like to think I've outlived that much immaturity."

He took in a breath, then swam downwards, wary of any stray tentacles. But the creature seemed to be still. For now.