Animals are mostly impulsive and follow instinct, but they still have a level of 'sentient' to them...Humans, by definition are: a bipedal primate mammal of the genus Homo.
So if you look at it that way, humans are monkeys that walk on two legs. But over time human has become so much more because we take 'sentient' to a whole other level. We don't just learn over one of our lifetimes. The whole human species learns as a whole, over time, and changes. Is this evolution or a human only trait? I'm not sure. But our ability to remember, create, think, and develop in full is much broader a trait than the same thing in any other animal.
To be human, you must be born from a human and posses human traits. Thinking like a human is optional (think of those who are brain dead...they are still human).
The real question is: are humans any more special than the animals around them?