English Idioms and Idiomatic Expressions 

Body idioms relating to Back, Belly and Stomach
from: 'behind someone's back'   to:  'cast-iron stomach'

BACK

• behind someone's back
  • If you do something behind someone's back, you do it without letting them know about it, in a way which is unfair.
    "I bought the car behind his back and now he's really angry."
    
    
• break your back
  • If you work extremely hard, or put a lot of effort into achieving something, you break your back to do it.
    "If you want the job done well, you should accept to pay more. He's not going to break his back for such a low price!"
    
    
• get off my back!
  • If you tell someone to get off your back, you are asking them to stop finding faults or criticizing you.
    "Liz, please, get off my back! You've been making comments about my work all morning!"
    
    
• have your back to the wall
  • If you have your back to the wall, you are in serious difficulty
    "With his back to the wall, the supplier had to accept the deal."
    
    
• keep your back covered
  • If you do something in case a problem might arise later, for which you might be blamed, you keep your back covered.
    "You'd better make a copy of that letter to keep your back covered."
    
    
• scratch someone's back
  • If you scratch someone's back, you offer to help someone if they help you.
    "If you find a job for my son, I'll vote for you. You scratch my back and I'll scratch yours."
    
    
• stab in the back
  • Someone who stabs you in the back, betrays you by doing something harmful to you when you thought you could trust them.
    "His best friend stabbed him in the back by voting against him."
    

• go belly up
  • If a business or project goes belly up, it is unsuccessful or goes bankrupt.
    "The restaurant went belly up before the end of the first year."
    
    
• (a) belly laugh
  • A belly laugh is a spontaneous, uncontrolled, hearty laugh.
    "The comedian hoped that his jokes would produce long belly laughs."
    
    
• yellow belly / yellow bellied
  • A person who is yellow-bellied is cowardly, or not at all brave.
    "The bus was full of yellow-bellied passengers who disappeared when the driver was attacked by two youths."
    

• (have) butterflies in your stomach
  • If you have butterflies in your stomach, you are feeling very nervous.
    "At the beginning of an exam, I always have butterflies in my stomach."
    
    
• (have a) cast iron stomach
  • If you can eat all sorts of food, and drink what you like, without any indigestion, discomfort or bad effects, it can be said that you have a cast-iron stomach.
    "I don't know how you can eat that spicy food. You must have a cast-iron stomach!"