One sure-fire way to tease and get a reaction from Joon is to sing a song that is off-limits. And of all the songs in the world, two rise to the top as VERY CLEARLY off limits: Let It Go and Paw Patrol. There are very specific (although changing) rules to these songs:
Let It Go, every single girl's favorite song in 2014. Only girls can sing that. Sometimes she will extend this rule to all women (so I can sing it, sometimes). If Murray tries to sing this, Joon first reacts by reminding him tersely of the rule: "Only girls sing that!" If Murray continues to sing it, then Joon's reaction quickly turns into real anger, screaming, crying, and in general an all-out highest-level protest.
Gulliver also knows this trick (as well as many other tricks that bug Joon) and will use it intentionally when he's in the mood.
Paw Patrol: This is the theme song to one of Gulliver and Joon's favorite shows. The rule for this song? "Only the pups sing that." Never mind the fact that Joon is a girl, not a pup. The funniest thing about this song is that it gets stuck in Murray's head. So it happens that SEVERAL TIMES A DAY, Murray starts singing, "Paw Patrol, Paw Patrol" and usually very, very quietly under his breath.
Joon hears it. Every time. Without fail. It doesn't matter how quietly Murray is singing it.
"ONLY THE PUPS SING THAT!!"
This has escalated to the point that Joon often simply chooses to HISS like a cat at Murray in warning, before giving him his verbal warning.
For the records of history, here are the words as sung by Joon: "Paw Patrol, Paw Patrol, be there on the double! W'ever there's a problem, 'round aventure bay, Ryder and his team of pups come and save the day! Paw Patrol, Paw Patrol, be there on the double!"
(Murray is sitting beside me as I write this, and he corrected me: "Only the pups CAN sing that." So as I was editing the post to reflect this correction, I sang loud enough for Joon to hear, "Paw Patrol, Paw Patrol..." Right on cue, she responded with "Only the pups sing that!" Thanks, Joon for the clarification. But in the next sentence she reminded us again, "Only the pups can sing that." So we are both right. Murray to his credit hears it WAY MORE OFTEN than I do.)