One way that Ava shows frustration (aside from screaming, spitting, licking, hitting, etc...) is this thing that she calls a "Grit." When she gets very angry, she will put her hands up into fists and make the most awful looking face. She knows how bad we hate it, so it is a way for her to press our buttons. Sometimes she will just come up to me and say, "Mommy, can I give you a grit hug." That is a hug in which she does a grit at the same time. She knows that you want a hug, but wants to see if she can push buttons and get by with it. What a little devil! I hope she grows out of this stage soon!
(And this photo doesn't even do "The Grit" justice!