Are they fools to throng together? (5,5)

I believe the answer is:

dense crowd

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'together?' is the definition.
I don't know anything about this answer so I cannot tell whether this works.

'are they fools to throng' is the wordplay.
'are they fools' becomes 'dense' (I can't explain this - if you can you should believe this answer much more).
'to throng' becomes 'crowd' (I've seen this before).
'dense'+'crowd'='DENSE CROWD'

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