Do you know a boer diff lock?

Some years ago I drove up a mountain with an elderly Afrikaans gent in his Toyota 1600 bakkie. It was in the Eastern Cape and we were on our way to go kudu-hunting. The road was wet and steep, and the bakkie didn’t have four-wheel drive, not to mention a diff lock. We crawled up the mountain. The man kept his right hand on the steering wheel with his other tightly gripping the handbrake. Every now and again he yanked on the handbrake and then accelerated, and soon I noticed a pattern in these actions. As soon as the bakkie started to struggle, he pulled on the handbrake, but it didn’t make any sense to me. When we got to the top, I was dying to know why he did it. So I asked and he calmly responded: “Have you never heard of a boer diff lock?” And suddenly the penny dropped... Today I drive an old 1998 Toyota Prado 90, also without a diff lock, but it has a boer diff lock that’s gotten me out of trouble many, many times.