Let's have a look at some Idioms using Body Parts:

Mouth -
Idiom: a big mouth
Meaning : To have a big mouth means to reveal any secrets
In a sentence: I'm not telling my sister about the surprise party. She has a big mouth and everyone will come to know!

Ears -
Idiom: walls have ears 
Meaning: Other people could be listening to what you're saying
In a sentence: Lower your voice and speak softly. Walls have ears. 

Nose -
Idiom: to have a nose for
Meaning: A natural ability to find or recognize something
In a sentence: Our boss has a nose for knowing when we're not working too hard.


Leg -
Idiom: pull your leg
Meaning: To tease or joke with someone
In a sentence: Don't take him seriously. He was just pulling your leg when he said he'd tell your dad you were out all night partying.

And for more on idioms...take the lesson It's Raining Idioms!