Looking for a native speaker's input for a research paper.

I'm currently writing a research paper on Japanese idioms for a linguistics class, and one component of the paper involves getting a native speaker's opinion on different words and phrases.

If any of you have a moment, could you tell me whether or not you know why the following idioms use the words that they do?

猫糞する
舌を巻く
猫に小判
判官びいきする
匙を投げる

Also, in the following compounds, do you know why the kanji that are used were chosen? Are the kanji in these words in any way related to the meaning of the word, or are they most likely 当て字?
十分
猫車
皮肉
茶番
空涙

Thank you so much for your help and your time!

I only know why 判官びいき has that meaning. I've never seen/heard 猫糞する and 空涙 before.