Mma Makutsi looked steadfastly ahead. They had now started their journey, and the makoro was heading upstream, throwing out a wake of crystal-clear water on either side of its narrow prow. The water glistened in the sun like a layer of liquid diamonds; beneath, some feet below, lay a clear sand-bank, mottled by the shadows of the wavelets. There was no sign of hippos just yet, but the river twisted this way and that, and there were many turns still to be negotiated. A herd of hippos might be behind any of these, waiting to demonstrate their well-known irascibility.

“I suppose it is better to be taken by a hippo than a crocodile,” the boatman went on. “If a hippo bites you in two, then you do not have much time to think. It is very quick … particularly if he gets your head in that big mouth of his. Then it must be like night coming suddenly. Very dark, I think, Mma.”

Mma Ramotswe tried to distract him. “There is a very interesting bird in the reeds over there, Rra. Did you see him?”

“That bird is very common, Mma,” said the boatman. “You will see many of those birds in the Delta. You must not worry about them. They are harmless.”

“I was not worried about the bird,” said Mma Ramotswe. “I was just pointing it out.”

“Of course,” went on the boatman, “if a crocodile gets you, then that is very different. That is not a good way to go. You’ve heard about the roll?”

Mma Ramotswe said nothing. Mma Makutsi was staring ahead; she too was mute.

The boatman was warming to his subject, raising his voice to make sure that both his passengers heard. “The crocodile gets you in his jaws. Then he takes you down under the water and he rolls over and over, spinning you round and round. This is to make you drown. Then he drags you away to his lair, which is usually under roots at the edge of a riverbank, rather like that place over there. See it? That is a good place for a crocodile to have his lair.”

Mma Makutsi did not dare so much as switch her gaze to the side; Mma Ramotswe glanced towards the bank, and then looked back ahead.

“Crocodiles don’t like fresh meat,” the boatman explained. “They much prefer to eat their prey when it’s a bit rotten. That is why they put you in their lair, you see …”

“Excuse me, Rra,” said Mma Ramotswe suddenly. “This is all very interesting, but I do not think that it is a good idea to tell people these things when they are on the water. There are some stories that are better told on the land.”

“Yes,” said Mma Makutsi. “That is true. We do not want you to speak, Rra. We are not in a mood for conversation.”