Can you watch more than one movie at the theaters if you buy a ticket for a movie?

I mean the ticket is already overpriced so I'm just saying why not get
what you paid for.
Can't someone just watch a movie, and then when its done, walk into
another movie? They never check for tickets and there's not any
employees near the doors usually.
What are the consequences that could happen?
What do you think about it, and have you ever done it?