There’s no denying that a great screenwriter can make or break a film, but it turns out that sometimes they’re not the only ones who deserve the credit. Some of the best lines in movie history were actually improvised by the actors who spoke them. How frustrating must it be for those poor screenwriters to slave away on a script, only to have someone else come in and make up the perfect line off the top of their head. Well, their loss is our gain. Here’s a look at some of the best improvised moments in movie history…