Certainly the leopard is not big but it has a big heart. A fully grown male lion certainly is big, and its head is almost unbelievably large - as is its mouth when opened in a yawn. The rhino is more of an enigma than to look dangerous, and few hunters out here shoot them - only the Chinese sponsored horn poachers - which is a big problem in South Africa because we have so many white rhino. A sudden close encounter with a sleeping rhino when on a hike quickly dispenses one's false sense of it not being dangerous. I know that from personal experience.
A hippo is large and fat with an impressive head but looks too bulky to possess any agility - until you have seen it swing around and charge. Together with crocodile it still is the biggest killer of inhabitants of rural areas. The mass of a Cape buffalo is immediately evident but that is not intimidating in itself; what is intimidating is its aggressive disposition and facial expression - at best the disinterested way it looks at you, and at worst the unmistakable expression of utter revile which emanates from him - it is an aura of total contempt for your arrogance to be within its personal space. Robert Ruark said it first and I cannot express it neater: "He looks at you as if you owe him money".
Then there is the elephant. Those (at first sight by the visitor) apparently gentle giants who are so sure of themselves that they will walk a few yards past you where you are enjoying your sundowner, or reading a book in camp without even acknowledging your presence. One has to only once witness the immense strength of these animals to be really afraid of them. I firmly believe that no elephant has ever tested the ultimate ability of its power, considering the effortless ease with which even a young bull will flip a car onto its back. To see in a video the instantaneous anger of a cow that nonchalantly tosses a fully grown 1,800 lb. buffalo feet into the air because it had not moved out of the way of her and her calf. Or the effortless ease with which they can push over a huge marula tree to get to a few shoots of fresh leaves at the top and then casually walk on as if nothing more than simple foraging has happened.
It seems the hunters of old expressed their respect for these five animals by calling them "big" for the display of big character they possess to attack the hunter who did not display sufficient strength of character himself to kill it outright with a close-in brain shot. It seems they detest the cowardly 50 yard shot which is flinched into the lungs by a nervous hunter who should not have been there in the first place - because he relied on a heavy kicking magnum rifle and not on having the guts to come up close enough and kill it outright with a brain shot, and used a lesser cartridge that allows for perfect placement. It seems they detest the weakness of "buck fever" (which is the symptom of the lack of an instinct for resolute killing) and which causes flinching, and decide that after that insult to them you need to be tested and punished - and may the best man win.
Rhino is not included in my own assessment as they are not much hunted. South Africa is a successful conservancy of rhino with about 25,000 in state and private game reserves and supplies the whole of Africa with rhino and then these get poached by Chinese operators almost immediately. The past 10 years or so more than 10,000 rhino have been poached here as well for the horns; the prognosis of where the international top level of this criminal activity resides is not a pleasing finding.
You want to stop the brain from functioning within seconds after the shot by stopping the heart - if it had not been a brain shot in the first instance. I do not even carry expanding bullets in Mozambique because from .35" and wider e flat mephlat bullet already creates a 4x calibre wound channel inside the animal.