Looking up a word that you don't know while reading a book. There's no movie equivalent. You never have to pause a movie cause you don't understand and consult another different movie.

The closest thing is when you're watching a movie and you see someone who you recognize from another movie but you can't remember their name. It doesn't really impact your ability to understand what's going on, but it's distracting enough that I can't move past it.

IMDB is like the movie dictionary.