In the scene where Sean starts talking about his dead wife and her farting antics the lines were ad-libbed by Robin Williams, which is why Matt Damon is laughing so hard. The scene took everyone by surprise. According to Damon in the DVD commentary, this caused the cameraman to laugh so hard that the camera can be seen moving up and down slightly.
I think the fact that nearly every single post on my dash is about Robin Williams is a testament to how great of an actor he was and shows just how many people he inspired/how many people loved him and his work.
Still in shocked and heartbroken by this news. Like many 90s children, I grew up watching Flubber , Mrs.Doubtfire and graduating onto his other works such as Dead Poet’s Society. Williams was and will always be a creative and comic genius.