Once the grains of sand have fallen through the mitotic hourglass, there's no point in turning it over again. 一旦有丝分裂沙漏里的最后一粒沙落下之后，重头再来一遍也就没什麽意义了。
Nothing you or I could do would make more than one grain of sand pass through this narrow neck without impairing the hourglass. 在不损坏沙漏的情况下，不管我们怎么做，都不能让两粒沙子同时通过狭窄的瓶颈。
