watch one's dust v. phr.,
slang To notice your quick action; watch you do something quickly.
Offer Bill a dollar to shovel your sidewalk, and watch his smoke! "We'll have your yard cleaned in a jiffy," the Boy Scouts told Mr. Truitt. "Watch our smoke!" "I can go to the store and be back in five minutes," bragged Tom. "Just watch my dust." [TahlilGaran] English Idioms Dictionary ▲