Thank you jusko88. Considering it was done without a tripod I'm okay with the results. I very rarely use tripods, although I have a couple of them. I know, the quality of results over handheld is remarkable. I just hate lugging them around all day.
I think Blackduiker took the photo right when the leopard was about to close/open its eyes, so what you see it's the nictitating membrane (inner eyelid).