Idioms

Teaching definately brings a bunch of new information about language that I find myself quite surprised once in awhile.
Today I've decided to bring up a few idioms in English...it's funny coz we're so used to say idiomatic expressions in Portuguese...and translating them to English would just be a mess...and so the opposite way round.
There were a few expressions tha I can certantly say that I've never heard it...not in English neither Portuguese... " on the grapevine"..."to let the cat out of the bag"..."a feather in your cap"..."can't hold a candle to (someone)"..."worth its salt"...etc...
So, now that I have done my "homework"...i'd like to know...have you ever heard this expressions?? Do you know its origin? You're not supposed to check its origin on the Internet, ok??? I promisse to post the answer next week!!!!!

Love you all!!! I'm wearing my heart upon my sleeves!!!!