Sentence:  Mrs. Terrapin, having selected a place to her liking, moistens the hard clay, then alternately with the sharp claws of her hind feet, begins scraping out a hole about two inches across, lifting the moist earth, <WSD>footful</WSD> after <WSD>footful</WSD>. 
Meaning of the word marked with <WSD> tags:  An amount that can be picked up by one foot.