Why Do Actors Pause When Talking?

I notice in films, TV etc, some actors say a line then pause for a second or something and say the next line Such as in my favourite Star Trek episode 'Balance Of Terror' The other ship has fired at the Enterprise and it is getting closer Yeoman Rand says to Cpt Kirk (William Shatner) 'Captain... show more I notice in films, TV etc, some actors say a line then pause for a second or something and say the next line

Such as in my favourite Star Trek episode 'Balance Of Terror'

The other ship has fired at the Enterprise and it is getting closer

Yeoman Rand says to Cpt Kirk (William Shatner)

'Captain should I continue log entries'

Then William Shatner as Kirk looks at her and says

'Yeoman........(pauses)........then looks at the screen and then says

'affirmative continue log entries'

Marlon Brando paused to give him.time to read the next cue card but what about real actors who learn all lines like Shatner, what is the point in pausing while saying a line?
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