Because if cows hear the ranch hands say 'calf tie' they run away. But if they think they're coming for the swine, they just stand around casually chewing their cud and farting great big holes in the ozone layer while they wait to watch the hogs get roped.
How do you know if you've run out if disappearing ink?
That's actually a misnomer, it's supposed to be "shy" foxes, but foxies are too timid to correct anyone so they let the term "sly" stick. They also figured out the term raises the level of respect they get from their fellow forest dwellers so it's all good...pretty slick huh? Hmm, maybe they really are sly after all!