For checking the transcript: https://www.buzzsprout.com/2379282
When pigs fly
 is used to describe something that will never happen or is extremely unlikely to happen, often in a humorous way.

Examples:
1- My friend said she’d give up online dating for good. She’s always on the apps, so that’ll happen when pigs fly!
2- Some people hope for a world where everyone gets along and all conflicts, including wars, are resolved, but that will happen when pigs fly!