If two people are at cross purposes, they think they are talking about or trying to do the same thing as each other, but they are actually talking about or trying to do different things. They had been talking at cross purposes earlier, he realized. They hadn't been offering him a share of the deal at all.

If you come out of your shell, you become less shy and more confident.

n o t e The image here is of a snail or shellfish, both of which go into their shells fo r protection. She used to be very timid and shy but I think she's come out of her shell.

n o t e You can say that someone or something brings you out of your shell when they cause you to be less shy and more confident. I think the job has brought her out of her shell. 

If two people or groups who generally disagree find common ground, they find a particular subject or opinion that they agree about. Both leaders were keen to stress that they were seeking to find common ground

If you get a piece of information from the horse's mouth, you get it directly from someone who is involved in it and knows the most about it.

n o t e This expression may refer to the fact that you can tell a horse’s age by looking at its teeth. When he tells them, straight from the horse's mouth, what a good assistant you are, they'll increase your wages. 

If you get your wires crossed or get your lines crossed, you are mistaken about what someone else means.

n o t e People used to say they had a crossed line when their phone call was connected wrongly and they could hear someone else’s conversation. She looked confused at what he said and he began to wonder if he'd got his wires crossed. He'd got his lines crossed: 'What part of America are you from?' he asked. 'Sweden,' came the reply

If a person or piece of writing goes off on a tangent or goes off at a tangent, they start saying or thinking something that is not directly connected with what they were saying or thinking before.

n o t e In geom etry, a tangent is a straig ht lin e w h ich touches a cu rve at one p oin t. Our teacher would occasionally go off on a tangent and start talking about something totally unrelated to the textbook.

n o t e You can use other verbs instead of go. The book's theme wanders off on a tangent now and then. 

If you hear something through the grapevine or hear something on the grapevine, you are told a piece of news informally by someone who was told it by someone else.

n o t e One of the early telegraph systems in America was given the nickname ‘the grapevine telegraph’ because the wires often became tangled, so that they reminded people of grapevines. I heard through the grapevine that she was looking for work. She heard on the grapevine that he had come back to London

If you say that something is in black and white, you mean that you have written proof of it. We have a strict, clear rule in black and white, that this sort of behaviour will not be tolerated. 

If someone is in the loop, they are part of a group of people who have information about a particular thing. Not many people knew what was going on but the president was almost certainly in the loop

If you keep someone posted, you continue giving them the latest information about a situation. She made me promise to keep her posted on developments here while she was in London. 

If you let the cat out of the bag, you reveal something secret or private, often without meaning to.

n o t e Perhaps from an old trick where a person pretended to sell a piglet in a bag, although the bag really contained a cat. If the cat was let out of the bag, then the trick would be exposed. 'They didn't tell the cops my name, did they?' 'Of course not,' she said. 'They wouldn't want to let the cat out of the bag.' 

If you put someone in the picture, you tell them about a situation that they need to know about. I believe that I could now produce evidence to prove my case, so let me put you in the picture.