Smell a rat

To say "I smell a rat" means that you suspect that something is wrong, or that someone is doing something dishonest or incorrect

Same boat

If two or more parties in the same boat, they are in the same unpleasant or difficult situation
 Example:  When the factory closed down, the workers all found themselves in the same boat

Scratch the surface

When you only scratch the surface of a problem or subject, you deal with only a small part of it
Example:  Some countries are only scratching the surface of their environment   problems

Second nature

If something you do is second nature to you, it is something that you do easily or automatically because you have done it so often or for so long
 Example:  Skiing is second nature to Harry.  He grew up in a ski resort

Sell your soul

This is a humorous way of saying that you would be willing to do something morally or legally wrong to obtain what you want
Example:  He'd sell his soul to get an interview

Sink or swim

 If somebody has to sink or swim, they have to do something alone and their success or failure depends entirely on their own efforts
 Example: the sink or swim attitude in the company can be very difficult for   young recruits

Stand up for
 someone or something

When you defend or support a person, a belief or an idea, you stand up for them
 Example: A growing number of citizens is standing up for the victims of discrimination

Swallow your words

If you swallow your words, you admit that you said something wrong
 Example: He said I'd never get the job, but he had to swallow his words when I was appointed