“More likely the first explanation,” Crowe said. “It’s called 'the drunkard’s walk', an’ it’s actually a good way of coverin’ ground quickly if you’re lookin’ for somethin’. Most people, searchin’ an area, will just walk in straight lines, criss-crossin’ it, or divide the area up into a grid an’ search each square separately. Those techniques will usually guarantee success, eventually, but the chances of findin’ whatever it is quickly are increased by usin’ this random way of coverin’ the ground. It’s called 'the drunkard’s walk',” he added, “cos of the way a man walks when he’s got a bellyful of whisky — legs goin’ in different directions to each other and head goin’ in a different direction entirely.” He reached into his jacket pocket and removed something. “But back to the ants: once they find somethin’ of interest, watch what they do.”

He showed Sherlock the thing in his hand. It was a pottery jar with a waxed paper top held on with string. “Honey,” he said before Sherlock could ask. “Bought it in the market.” He pulled the string off and removed the waxed paper. “Sorry if this brings back bad memories.”

“Don’t worry,” Sherlock said. He bent down to kneel beside Crowe. “Should I ask why you’re wandering around with a jar of honey in your pocket?”

“A man never knows what might come in useful,” Crowe said, smiling. “Or maybe I planned all this in advance. You choose.”

Sherlock just smiled and shook his head.

“Honey is largely sugar, plus a whole load of other things,” Crowe continued. “Ants love sugar. They take it back to the nest to feed the queen, and the little grubs that hatch from the eggs.”

Dipping his finger in the honey, which Sherlock noticed was runny in the heat of the morning sun, Crowe scooped up a huge shiny droplet and let it fall. It caught on a clump of grass and hung there for a few moments before strands of it sagged to the ground and lay there in scrawled and glistening threads.