It literally means “take the soup out”. And its an expression used to express you are making someone tell you something they usually wont, something they don’t want to, or something someone else is reclutant to tell you.
Voy a sacarle la sopa sobre como consiguio su fortuna / I’m going to make him tell me how he got his fortune.
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I hope you have learned something new, about the spanish that real Mexicans talk on their everyday life.
If you want to improve your Spanish, I also give tutoring lessons on skype using this page that host many teachers from all over the world, and while I don’t really do grammar, I can help with conversation and doubts about the language. Also, if you are interested in any language besides spanish, there are teachers and tutors for any language there.