In order to air properly on commercial television, all the episodes of the He-Man cartoon series were written and filmed to specific running times: the first and second acts ran for a combined total of twenty minutes and ten seconds, and the tag at the end ran for thirty seconds more.
The makers of He-Man used these tags as an opportunity to present short "morals" to the episodes. In the best of them, the morals were surprisingly wise and related directly to the story told (such as "Teela's Quest" and the moral about what makes a parent your parent, or "Trouble in Arcadia" and its unexpected description of the Magna Carta). All too often, however, the writers took the easy way out and presented simple, condescending morals that had no real relation to the episode. "House of Shokoti Part One", for example, had a moral where Ram-Man tells the viewer that "Rammin' things with your head... is just dumb!"; "The Taking of Greyskull" had a complex plot involving Greyskull's disappearance, and featured He-Man pursuing Skeletor all the way to Skeletor's home dimension, yet the moral they came up with to end the episode was this: "Don't get carried away with sweets".
My friends and I began referring to these collectively as "Don't put mustard on the cat" morals, often going so far as to shout, "And don't put mustard on the cat!" at the screen in unison after a particularly insipid episode had aired. It was only a matter of time, I suppose, before we felt compelled to script it.
FADE IN: EXT. ETERNIAN COUNTRYSIDE - DAY Teela and Battle-Cat, on a picnic. Teela holds up a jar of mustard. TEELA Heeey, Battle-Cat - look what I found. A jar of mustard! BATTLE-CAT (with a loud growl) Rraowr! Don't put that stuff on me! He-Man steps into shot, facing camera. HE-MAM (as he enters, to Teela) That's right - you'd better not do that. (to the camera) Of course, the cats on your world can't talk - and they probably wouldn't rip your lungs out, either. But still, putting mustard on the cat is a bad idea. You know, lots of boys and girls have been hurt - even killed - by putting mustard where it didn't belong. Don't put mustard on the cat! If you're not sure you can handle it safely, ask your mom and dad to help. (turning, he takes the mustard) I'll take that jar, Teela. TEELA He-Man! Thank goodness you're here. HE-MAN Glad to be of help. They all mug for the camera as we FADE OUT.