Not specific at all, but the sudden change in demeanor and the apparent inability of most people to read feline body language would likely result in a lot of them getting killed if it were not for the fence. That or turning their back, which the tiger is exceedingly partial to becoming aggressive toward. He becomes, from one moment, tolerant and perhaps even social, to crouching and quickly stalking - getting as close as he can manage to his fence line and nearly pressing his muzzle to the metal or ports.