. . . watching the audience return . . .

[shootingstar]

The tables and chairs of the two kitchens are still on the stage.
The ladders and the small bench have been withdrawn.
The STAGE MANAGER has been at his accustomed place watching the audience return to its seats.
(Thornton Wilder, Our Town, Act II, stage direction)

What part of speech is the word return there? It puzzles me

 

[5jj]

It's a bare infinitive.

 

[shootingstar]

Yes, thank you, I understand now. The bare infinitive is due to the verb watch: you can say watch somebody/something doing something but you can say watch somebody/something do something as well. Is there any difference in meaning?

 

[Barque]

Is there any difference in meaning?

Not necessarily but there can be. It depends on what the 'something' is.

I watched him dancing. This means you watched him while he was dancing. You may or may not have watched him from start to finish.

I watched him open the bottle with his teeth. You watched the entire act.