A nail in someone or something's coffin is a problem or event that is a clear step towards an inevitable failure.
If a game, election, contest, etc, is a nail-biter, it is exciting because the competitors are so close that it is impossible to predict the result.
This idiom is used to express the idea that empty or unfilled spaces are unnatural as they go against the laws of nature and physics.
The basic characteristics of something is the nature of the beast; often used when there's an aspect of something that cannot be changed or that is unpleasant or difficult.
If something is near the knuckle, it is bit explicit or too close to the truth for comfort
Difficult situations make people inventive.
If two competitors or candidates, etc, are neck and neck, then they are very close and neither is clearly winning.
Subjunctive (I suggest you do)