One of my chicks, an australorp pullet, not quite 3 weeks old, is showing some strange behaviour. In the last couple of days, I have noticed her sitting/squatting/crouching so that her lower legs are touching the litter, then she'll rock back on her knees(?). Sometimes she'll catch herself, and other times she'll fall over, usually to the right. I picked her up, and her rear is clean as a whistle. She will scurry around with the rest of the chicks when I come to feed them (they tend to run away). Her appearance seems fine, maybe just a wee tad scruffy/rumpled. I guess I should spend more time with them to see what her eating habits are. Does anybody have any ideas what might be causing this, and if it is critical?