Sentence:  I stay with Chloe the longest. When she's not hanging out at the beach parties, she lives in a Japanese garden complete with an arched bridge spanning a pond filled with koi of varying sizes and shapes. Reeds shoot out of the water, rustling when the fish swim through them, and river-washed stones are sprinkled in a bed of sand. Chloe has this whole new Japanese thing <WSD>down</WSD>. 
Meaning of the word marked with <WSD> tags:  Thoroughly practiced, learned or memorised; mastered. (Compare "down pat".)