The idiom "don't look a gift horse in the mouth" means that one should not question or examine something that has already been given or offered, especially when it comes to accepting a favor, service, or reward.

The idiom "mull over" means to think about something carefully, typically before making a decision or taking action. It can also mean to consider or contemplate something deeply.

The idiom "the other side of the coin" refers to a perspective or point of view that is opposite or different from the one being discussed or considered. It can also mean a situation or outcome that is the exact opposite of what was expected or hoped for.

The idiom "a man of action" refers to a person who prefers to act on their ideas rather than just talking about them. It describes someone who is capable of taking decisive and practical steps towards achieving their goals, instead of simply theorizing or planning.

The idiom "nail in the coffin" is used to describe a final action or event that puts an end to something, typically a situation, relationship, or plan. It often implies that this action or event was waiting to happen and it has now been confirmed or cemented.