The idiom "red herring" refers to something that is introduced or presented as a distraction from the main issue or problem being discussed. It is often used to refer to a false lead or a diversion that is meant to confuse or mislead people.

The idiom "dead as a dodo" means to be completely dead or lifeless, with no movement or activity whatsoever. It is often used to describe someone who has died or passed away.

The idiom "there's no such thing as a free lunch" means that nothing is truly free or without cost, and that there is always some form of compensation or benefit expected in return for something.

The idiom "water under the bridge" means that something has happened or occurred in the past, and it's not relevant to what is happening now or in the future. It's a way of saying "let's move on from the past.

"All that glitters is not gold" is an idiomatic expression that means something may appear attractive or valuable on the surface, but it may not be worth the effort or money to pursue it further.