Most girls are sensitive and can tell that a guy likes him, but it's possible that she is face-saving and will pretend not to know. And a small number of girls may be nervous, usually not so careful, not aware of boys like her, which requires boys to show more obvious.
Most girls are more sensitive, also very easy to meet, as long as you pay attention to the boys' expressions, actions will find that some of the same, so she can perceive that boys like her, but girls love face, will pretend not to know, you ask her will not be clear, do not know, vague in the past, so boys want to catch up with girls, you must do something to let her move.
And in reality, there are indeed some big nerves, usually not so careful girls, then she may not be aware of boys like her, which requires boys to show more obvious, do more to surprise her, moved things, it is best to be able to directly to her.