The best way to learn proper English is to read news report, and watch news on TV. Watching TV shows is a great way to learn casual English, slang words, understand culture reference and humor. If you have already watched these shows then you may recall the words used in the following dialogs.

(MOCKINGBIRD continues singing)
The Big Bang Theory Season 5, Episode 17

(MOCKINGBIRD whistles)
And you...
The Big Bang Theory Season 5, Episode 17

That's a MOCKINGBIRD.
The Big Bang Theory Season 5, Episode 17

A MOCKINGBIRD.
Game of Thrones Season 2, Episode 1

(MOCKINGBIRD whistling)
The Big Bang Theory Season 5, Episode 17