People in here don't have much knowledge of the animal kingdom. I chose the gorilla because you can stand very still and keep your head down, whatever you do, don't look it in the eye. Once it has finished its charge(a very scary moment) Do not run for fucksake. Chances are the gorilla will accept your submission and leave you alone.
A lion however and a bear will be attacking you for food. You can bluff a lion maybe if it is one out in the wild, Native hunters have done this to poach from a pride's kill. It is very dangerous and they usually work out fast that you aren't the dominant predator. Hunters usually bail fast like after cutting from the carcas. Usually involves walking slow, head held high, no sign of discomfort, A mind game.
Loud noise in a random encounter might confuse them enough to briefly go away but you better have a good exit strategy.
Fuck the grizzly you got no chance.