在实验中切不可粗心大意: do be careful with the experiment you're doing
火车切不可越过危险信号: a train must not pass a signal that is at danger
孤注一掷: throw the helve after the hatchet; bet all on a single throw; bet one's bottom [last] dollar on ...; go for the gloves; go nap over ...; have [put] all one's eggs in one basket; make a las
切不可作任何损人利己的事: never do anything to your profit at another's expense
