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!

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。

youdao

When a blind man just caught big gun, flash box on my cousin, said: hey, what to buy a bottle of orange?

当瞎子刚刚抓住一盒闪光炮时，大表弟在一旁说：嘿，买什么炮竹？

youdao

Hey, big man, a voice said.

NEWYORKER: Uncle Rock

Embarrassing moments such as asking for a bigger pants size and having a homeless man yell, "Hey, big guy!"

CNN: Tired of slights, embarrassment, man sheds 87 pounds