This week, the theme for Wanderer's Thursday Movie Picks Meme is non-musical films that have a scene where characters break into song. This is certainly an unusual choice for a category. It's hard to think of films that have a musical number without accidentally going back to musicals.
For this list, I have made sure to include images of the musical numbers from each film so that it is clear what I'm referring to.
Monty Python and the Holy Grail (1975)
Monty Python has occasionally delighted in enhancing its already bizarre comedy with surreal musical numbers. Monty Python and the Holy Grail does this memorably early on. King Arthur has assembled his knights, and introduces them to Camelot. Cue a bizarre musical number about being Knights of the Round Table. It's not even clear exactly how this classic sequence fits into the diegesis of the world (whatever it is, it's apparently enough to convince Arthur that Camelot is "a silly place" and that his knights should avoid it). This is the only real musical number (other songs featured, such as "Brave Sir Robin," don't have the same flare). The number primarily features singing and dancing knights around different parts of the castle's great hall. They dance around and knock over silverware. At one point a peasant plays a percussion solo by striking several knights with a ladle (and hits a peasant by accident). They even have a prisoner in the dungeon who claps along to the merriment!
The film also makes a joke about musical numbers during its "Tale of Sir Lancelot" segment. This section follows Prince Herbert, who is trapped in an arranged marriage with a princess. Throughout the segment, Herbert keeps trying to break into song only for the music to be abruptly stopped by his father (who is very adamant against him doing a song). This also results in an interesting touch when Herbert manages to start a musical number at the end of the section (to his father's irritation), and we still never hear him actually sing anything
History of the World: Part I
Mel Brooks' bizarre mock-historical drama provides a variety of peculiar sequences depicting outlandish interpretations of famous events, but special mention goes to a very bizarre sequence where we are introduced to the Spanish Inquisition. This infamous organization known for its ruthlessness and cruelty is represented by... an upbeat and extremely cheerful musical performance where Brooks himself plays their musical number. Lots of weird choreography ensues as the Inquisition very cheerfully tries to force its prisoners to convert.
Austin Powers in Goldmember (2002)
The third and final installment of the Austin Powers series of James Bond spoofs features a very weird musical number that marks an especially weird moment in what is already a very surreal and nonsensical plot. Professional bad guy Dr. Evil (Mike Myers) has been thrown into prison by the hero (also played by Mike Myers) and tries to devise an escape plan. His plan amounts to getting every other prisoner to start a riot so the guards don't notice when he and his sidekick Mini Me walk out the front gate. To get them motivated, he performs a bizarre hybrid of lip-syncing "It's a Hard Knock Life" and rap verses.