Emotionally, Huck varies between being a typical young boy and a more mature adolescent. In the graveyard, he shows the young boy side, getting scared and reacting quickly and emotionally to the uncertain:
Presently Tom seized his comrade's arm and said:
"What is it, Tom?" And the two clung together with beating hearts.
"Sh! There 'tis again! Didn't you hear it?"
"There! Now you hear it."
"Lord, Tom, they're coming! They're coming, sure. What'll we do?"
"I dono. Think they'll see us?"
"Oh, Tom, they can see in the dark, same as cats. I wisht I hadn't come."
However, later in the novel, Huck shows that he is rational. He understands that he is an outcast, and while he accepts it, he is hurt by it, because he feels that he can do no right:
"Well, you see, I'm a kind of a hard lot,--least everybody says so, and I don't see nothing agin it--and sometimes I can't sleep much, on account of thinking about it and sort of trying to strike out a new way of doing. That was the way of it last night."
Twain sets up Huck as a complex character, more developed emotionally and intellectually than Tom, mostly as a result of the hard life he has suffered from. See the enotes.com link below for more information.