@MrsPramm - That's generally known as the Turing test and it's one of the goals that any intelligence would have to reach to be considered intelligence. The Turing test is basically that the computer program should be able to converse with a human in such a way that the human wouldn't be able to tell whether they were talking to a machine or a person.
I've never really thought about it, but I suppose that really is just cosmetic though. The average person might not know what kinds of things to talk about to really probe whether or not a computer is able to keep up the deception. And there is the question of what sentience actually is in the end. Just because something seems sentient doesn't actually mean that it is.