Thank-you all for the lovely comments.
The lion was interesting because we sat watching her for about three hours. In this particular shot she is very interested in two zebra that came to drink - that is why she is staring so intently in their direction. I thought I was about to hit the jackpot with a chase and a kill, but the zebra saw her and made off rather rapidly.
A while later some impala came to the waterhole but were scared off by the ill-timed arrival of a bunch of cars.