MY FRIEND BEN and I were walking through the dusty scrub along the high banks of Zambia’s Luangwa River when our safari guide, Deb Tittle, stopped to confer with our rifle-toting scout. A moment later, we were following her down a steep embankment to the river’s sandy shore, not far from where crocodiles and hippos lurked in the shallow, muddy water. Ms. Tittle dropped to her knees and burrowed a hole in the sand, then dug another nearby. Looking up at us triumphantly, she invited Ben to reach in. He did, and gingerly removed an off-white egg, a little bit larger than the jumbo variety you might buy at the grocery store.