Who puts his hand on Jan's shoulder while he is reading a map?

From the text:

‘On Wednesday I was sitting in the jeep with my driver, studying a map. I had a cigarette in my mouth and was about to light it, when a hand slid over my shoulder, clapped on my lips and tweaked the cigarette out. I looked round and saw a'chimpanzee jumping up and down on the back seat, with the cigarette in his mouth.