I believe the give-away was that he clasped his legs together to catch something dropped in his lap instead of spreading his legs to make a net out of the dress. I was always doubtful of the realism, but I believe that's whats in the story.
... And when you throw at a rat or anything, hitch yourself up a tip-toe, and fetch your handup over your head as awkward as you can, and miss your rat about xix or seven foot ... And mind you, when a girl tries to catch anything in her lap, she throws her kneww apart; she don't clap them together ...
He also threaded a needle the wrong way.
We both were almost correct, but the book is so good that it's always a pleasure to find the place and quote it exactly - it's very much on topic of this thread:
And don't go about women in that old calico. You do a girl tolerable poor, but you might fool men, maybe. Bless you, child, when you set out to thread a needle don't hold the thread still and fetch the needle up to it; hold the needle still and poke the thread at it; that's the way a woman most always does, but a man always does t'other way. And when you throw at a rat or anything, hitch yourself up a tiptoe and fetch your hand up over your head as awkward as you can, and miss your rat about six or seven foot. Throw stiff-armed from the shoulder, like there was a pivot there for it to turn on, like a girl; not from the wrist and elbow, with your arm out to one side, like a boy. And, mind you, when a girl tries to catch anything in her lap she throws her knees apart; she don't clap them together, the way you did when you catched the lump of lead. Why, I spotted you for a boy when you was threading the needle; and I contrived the other things just to make certain.