Why indefinite articles?

Well, sort of, "perish the thought" does mean "absolutely not," but you almost always use it ironically when that's exactly what you did mean.

So let's say you made the crack about what I'll be wearing at the restaurant... and I say "Hey, are you making fun of me" (but I say it with a smile so you know I'm not really mad) you say "Perish the thought!" - as in "Oh, I'd never make fun of you, my good friend" - but you're being sarcastic, in a friendly way.

And yes, people will often say "perfect" when they mean the complete opposite.

But I'm not sure what you mean by "perfect illustration."

Thank you.

With all due respect, I am not here to crack up a joke but rather, to crack open a confusion in my mind as to be more clear on the following grammatical issue.

In regard to your sentence, "Was there anything else in that needs explaining," would you say it is more appropriate or even be right to say, "Was there anything else in there that needed explaining?"

I am asking this with all due respect.

    

Was there anything else that needs explaining?

fits into the category of the "past of politeness", in my opinion.

It is less direct than Is there anything else that needs explaining?, though it means the same thing.

This is a common formula where the direct question in the present tense seems too abrupt and insistent.

Compare:

Employee to boss:  I wanted to know if it's all right to take next Friday off.  (for I want to know ...)

CJ