I have problems with facial expressions!
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It's difficult because I sketch really sloppily and one ill--placed line can move the mood of a face entirely. Then, when I get around to cleaning up the sketch, I can't tell if (s)he was happy, angry, sad, or frustrated! xP

I don't try to hide it, I usually sort it out. The only thing I can do to fix it is to a) draw more neatly, and b) practice more exaggerated expressions. We shall see.