They carry the messages - the ones moving the theatregoers (8)

I believe the answer is:

trolleys

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'they' is the definition.
Both the answer and definition are plural nouns.
Maybe they are linked in a way I don't understand?

I don't understand the remainder of the clue.

Can you help me to learn more?

(Other definitions for trolleys that I've seen before include "They're to be found in hospitals and supermarkets" , "moving beds?" , "Shopping baskets on wheels" , "Shopping carts" , "Vehicles" .)

I've seen this clue in the Irish Times.

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