It is no easy thing to get at the meaning of every idiom.
2
要闹清楚每个习惯用语的意思是不容易的。
Not every idiom translates with such ease.
3
他使劲叫醒Bob,因为已经到九点半了,而Bob十点有数学大测验。时间紧迫,所以他要Bob必须立刻行动起来。 显然他说shake a leg,是催促Bob赶快行动。这就是这个习惯用语的意思。
3:Bob! Hey, Bob, wake up! It's already 9:30 and you've got that big math test at 10 o'clock. Come on, man, shake a leg! Come on, - you've got to get moving right now!