1. I don't like to eat popcorn at the movies.

2. I don't like to eat popcorn at the movie theater.
3. I don't like to eat popcorn at the cinema.
4. I don't like to eat popcorn in the movies.
5. I don't like to eat popcorn at the movie.
6. I don't like to eat popcorn in the movie theater.
7. I don't like to eat popcorn in the cinema.
8. I saw the actress in the moves or in the three movies.
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Does #1 mean #2 or #3? Why do we have to use the plural form 'movies'?
What is #4? Is it different from #1? Shouldn't we use 'in' in this case? We can use #8, can't we? What about using 'in' as in #6 and #7? In means 'inside', so we can use 'in' in this case. Am I right?

1, 2, and 3 all mean the same thing. Saying 'at the movies' vs 'at the movie' specifies that you are referring to the general place versus one specific event. 4 is awkward because when we say 'in the movies' we mean the in recording that is being played on screen not in the building that plays movies. 6 and 7 are understandable because 'movie theater' or 'cinema' cannot be confused with the on screen recording.