Visually, how does Sentinel reduce a creature’s speed to 0ft?

@LeMarcSharma @JeremyECrawfordVisually, how does Sentinel reduce a creature’s speed to 0ft? Would that work on Flying Swords (has speed 0ft)? ferocious blow knocks target off balance, ruins movement #wotcstaff

— (((Mike Mearls))) (@mikemearls) October 15, 2016