When Ken finally gets revenge for Wanda the fish, and loses his stutter.
A Fish Called Wanda was so funny it literally caused a Dutch man to die laughing from it. The man's *wife* held no ill will over it, basically because he died happy. It's a little morbid but quite touching, in a way.
Another real life one: playing Ken caused Michael Palin to start considering how hard it must be to have a stutter, and he founded a charity devoted to curing them.
John Cleese loved working with Michael Palin (already a frequent collaborator), Kevin Kline, and Jamie Lee Curtis so much that Fierce Creatures was made simply because he wanted to bring them back together again.