"Makes a Stink" is the ninth episode of season four and the forty-eighth episode overall of the animated children's series The Magic School Bus. It originally aired on November 30th, 1997.
It's the first annual Smell Search at Walkerville Elementary, and smell expert Flora Whiff is looking for the perfect scent. Carlos thinks he's found it with a mothball. But when he brings it to school, it's accidentally stepped on by Janet after Carlos drops it caused by Wanda.
So the class tries to search another smell, and Dorothy Ann suggests the class should use cinnamon, which she brought. Carlos, however, rebuffs this idea, stating that half the school already brought cinnamon. Just then, Ms. Frizzle offers them various of smells the class all brought inside bottles: Phoebe's mint, Ralphie's socks, Wanda's banana, Tim's rose, Dorothy Ann's cinnamon, Keesha's rotten eggs, and the smell from Pong the skunk in a cage. While the class takes a whiff of some of the bottles of smell, Dorothy Ann asks Ms. Frizzle how the smell of the cinnamon got inside the bottle without adding the sticks. So Ms. Frizzle offer the class Smell-a-visors to see the smell and the class puts hem on to see the smell of mint emerging from the bottle. On Ms. Frizzle's orders, they also put their Smell-a-visors to magnifier mode to take a closer look at the molecules of the smell. Dorothy Ann reminds the rest of the class about the molecules they learned before and how they work (from the episode Meets Molly Cule). She uses her cinnamon sticks to take a closer look of the molecules from the scent of the sticks and notices that they are shaped differently than the molecules from the mint's scent. When Tim realizes that when the mint and cinnamon scent mixed together, they make a different smell. Arnold then gives Carlos an idea to mix smells together to make a new smell using a smell mixer. Using a mint leaf, banana, cinnamon, and a sock, the class is satisfied of the smell and decides to use it for the Smell Search.
When asked by Dorothy Ann how the molecules make the smell, Ms. Frizzle shrinks the class and herself to size, as well as the bus, and they catch Janet sneaking inside the classroom and sniffing their mixture of smell. So the bus flies in front of Janet's face and enters the inside of her nose.
Inside, Carlos is able to smell the class' mixture and Ms. Frizzle tries to get the class out, only to get stuck by snot, which Carlos jokingly states, "It's snot!", to which Arnold asks "It's not what?" and Carlos corrects him with "Not 'what', Arnold, 'snot!", prompting the entire class sans Arnold to groan "Carlos, yuck!". Dorothy Ann reads in her book that snot (also called mucus) is a slimy liquid made by the nose to trap dirt and germs to prevent them from entering one' lungs. While Janet tampers with the smell bottles and sniffs a bottle of roses scent, the class notices the scent entering the nose and use their Smell-a-vision goggles to see the rose scent molecules. Ms. Frizzle also explains that each smell molecules has their own landing pad inside the nose, which is called a receptor. Dorothy Ann reads in her book that a human has thousands of different smell receptors that gives them thousands of different odors to choose from. When asked by Ralphie how the brain knows what the nose knows, Ms. Frizzle explains that a smell molecule travels inside a nose, lands onto the nose smell detecting receptor, and the receptor sends a message to the smell scenter of the brain. When Janet sniffs a bottle of scent from Ralphie's gym socks, the class take a glimpse of the molecules from the scent and Carlos finally realizes that Janet is trying to sabotage the class' winning smell. So he has Dorothy Ann and Wanda go out and help him wipe the mucus off the bus (but not before being offered anti-slime suits by Ms. Frizzle) and Janet decides to add the skunk odor to the class' smell mixture. When she takes a whiff of the skunk odor, it permeates inside her nose, and when she blows it, the class is blown out and onto one of the napkins Janet has blown her nose into right before she leaves the room.
While Flora Whiff is smelling the other students' bottle of smells at the Smell Search, the class is back to their normal size and they become distraught over the fact that Janet added skunk smell into their smell mixture. Dorothy Ann gets the idea to stop the skunk smell molecules from permeating Flora Whiff's nose to prevent her from catching a whiff of the smell since smell molecules take a while to travel inside the nose before they land onto the smell receptors. So while Janet and her class get a score of four and a half out of five at the Smell Search, Liz shrinks the bus (with Dorothy Ann, Wanda, Ralphie, and Tim inside) in size and flies it over the container with the class' smell mixture to prepare to eliminate the skunk smell molecules. As Flora Whiff finally takes a whiff of the smell mixture, the students inside the bus use the magnifier to see the skunk smell molecules and use the laser to zap the skunk smell molecules. When the judge is one, she gives Ms. Frizzle's class a score of a perfect five, much to Janet's surprise. The class tells Janet what they learned about smell and Ms. Frizzle states, "All's well that smells well".
- Flora Whiff is voiced by Bebe Neuwirth, known for her portrayal of Dr. Lilith Sternin on both Cheers and Frasier as well as Binky in Cyberchase.
- This is Janet's third appearance in season four, eighth overall.
- Arnold is one of the callers during the producer segment.
- This is Janet's final appearance in the original series.
- When Ms. Frizzle says, "Everyone say 'Stinky Feet'!", Wanda's Smell-a-visors are purple instead of bright yellow.
- Mr. Rhule is seen sitting on a chair on the stage floor in the auditorium.
- This is the third time the class goes inside a nose. The first is in "Inside Ralphie" and the second is in "Works Out".
- Surprisingly, Janet doesn't sneeze the class out like Ralphie did.
- This is the second time Janet doesn't show a moment of redemption. The first is in "Works Out".
- When Ms. Frizzle says, "To the odor-torium!", Dorothy Ann's Smell-a-visors are blue instead of purple.
- Going by production order, this is the 10th episode of Season 4.
- When Ralphie says "I can't believe Janet put skunk smell in here...but, she did!", his voice changes to Arnold's.
- When Carlos says "Let's try it.", Phoebe's Smell-a-visors are yellow instead of red.