When I did the Africa thing back in 2008, we drove around in a convertible land rover with our guide. He told us never to get out of the land rover, and had an interesting reason. He said that the animals are used to seeing the land rovers and just viewed them as some other big herbivore wandering around. But if we got out of the land rovers, all of a sudden there was some strange small creature there instead of a big herbivore that they see all of the time. So there's a chance that it could freak them out.
As an example, we were near some giraffes and there was nothing else around. He stopped the land rover and said, "Okay, get out." We got out and the giraffes freaked out and started running away. They were used to the land rover and it didn't scare them, but the second we hit the ground they were off and running. It was kind of cool.
With the big things like rhinos and cape buffalo, you figured that you were pretty safe even if they didn't like the vehicle. They can ram it, but as long as you don't fall out you're fine. The elephants could just reach in and pluck you out, but didn't seem to have any interest in doing so, even though a couple of times they were right next to us. We couldn't find any lions, but there was an enormous leopard at one point, and he was the most worrisome to me because you'd think a cat would jump right on board and drag you out. But he paid us no attention at all.
The funny thing was how we saw the leopard. He was resting under a tree, and another land rover saw him first and called our guide, so we went over there too. There were some giraffes in the area, and the first land rover saw the leopard because the giraffes were standing stock still staring at the leopard for the longest time. They didn't run, but they just stood there staring a hole through the leopard. It made it pretty easy to spot him.
Of course, after telling us to always stay in the vehicle, we at some point had a flat tire on a night ride and the spare didn't fit and the cell phones were in a dead zone, so we had to walk to a ranger station in the dark. That's a time when you keep your head on a swivel.