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- "Every good doctor knows: The best cure is complete rest."
- —Dr. Tennelli
"The Magic School Bus Inside Ralphie" is the third episode of Season 1 of The Magic School Bus. It originally aired on PBS on September 25th, 1994.
It's Broadcast Day and the class is counting on Ralphie to help them come up with an idea for the two hours of live television they're doing. The trouble is that he's sick, indicated by his coughing, so his mother, Dr. Tennelli, tells him that he can't go to school. So she calls Ms. Frizzle to tell her he won't be able to come, and Ms. Frizzle takes her class to Ralphie's house.
When Ms. Frizzle says that there is an amazing battle going on inside him, the class decides Broadcast Day should be about whatever is making him sick, prompting Arnold to say "I think Ralphie shouldn't have stayed home today." They go back to The Magic School Bus, making him believe they are leaving him. It later returns as a shrunken helicopter through his window. Ms. Frizzle tells him to say, "Ahh!," and it enters his mouth, approaching his red and swollen vocal cords, but he coughs, sending it flying out. Afterwards, it enters via a cut on his leg, to which Carlos jokingly says "It's a shortcut! Get it? Short cut?" causing the other students to groan "Carlos, yuck!". The Magic School Bus travels up his bloodstream to his throat. While watching a video of his bloodstream, he notices that the blood inside is clear rather than red and that the cells and red and white blood cells and the jagged cells are called platelets, which help the body heal scrapes and cuts. Meanwhile, Dr. Tennelli returns and notices the television. She remarks that the stuff on it is "remarkably realistic".
As The Magic School Bus enters the throat tissue, the students attempt to do the report. Ralphie and his mother watch this on television and notice that bacteria is destroying his throat cells, making him sick. Ralphie doesn't want her to know that the Magic School Bus and the students are inside him. Just then, the white blood cells come around and try to eat the Bus. Unfortunately, it multiplies and begins chasing the students. Dr. Tennelli then turns off the television and tells Ralphie that the best cure for a bacterial infection is complete rest. As she leaves, Liz turns it back on and the inside story continues, where the medicine Dr. Tennelli gave Ralphie earlier destroys the bacteria. The white blood cells also see the bus as a threat since it's covered with antibodies and attempt to devour it. The others call for help, but Ralphie doesn't notice since he's sound asleep. The bus barely manages to escape from the white blood cells' grip and ride off, with the white blood cells chasing after it. They make it to Ralphie's nose, and thanks to Liz banging a gong, he wakes up just in time to listen to the report on television.
The bus travels up his nose and Ralphie says “That’s the inside of my nose?” in surprise and adds “Weird”. After Liz tries tickling his nose with a feather, Ralphie initially tells her angrily that he's trying to think, but then says, “I get it — I got to sneeze them out” but then looks puzzled while adding “But I don’t feel like sneezing.”
Liz solves that problem by sprinkling black pepper in his face. The students, still small, are now back in his room and interview him. They tell him that his body is built to keep out things such as germs, his throat is sore because of his body sending extra blood there to fight off the infection, and the white blood cells almost ate the bus because his body thought it was bacteria. They also tell him that his body was doing all this to protect him.
As he finally gets some rest, the other students hop on the bus and leave through the window.
At the office, the male producer is using a stethoscope to listen to Liz's heartbeat, only to tell the lizard he can't hear anything. Just then, he gets a call from a girl who was wondering why the students would take a trip inside Ralphie's ill body, to which the producer responds he wasn't infectious. The producer then gets a call from a boy who reminds him that if the school bus could find its way through Ralphie's scab, then so could more germs. The producer agrees and states bandages are made not just to heal cuts and wounds, but to also keep germs out of the body as well. The boy also adds that viruses, parasites, and fungi are other diseases that could make a person sick. The producer also adds that some sickness is not only caused by infections, but also due to the body not working correctly. The producer later gets a call from the girl again, who informs that viruses can be dangerous and children should never take medicines unsupervised. The producer also informs that Ralphie became robust sometime after the episode. The girl then adds that keeping the body healthy should include things like eating better and exercising. The producer also adds that getting shots is another way to keep healthy, as they are to help the person be prepared for tougher germs. When asked if Mrs. Frizzle ever gets sick, the producer replies "no" and says Mrs. Frizzle takes care of her body and is magic. When she is shown through the computer screen, Liz reaches over and gives the screen a kiss.
- Ralphie's illness and the medicine his mother gives him are not specified in the episode, however the illness may very well be strep throat, with the bacteria being streptococcus ("coccus" means "ball" and "strep" means a long chain). The medicine is most likely an antibiotic.
- Music from the Producer Segment is reused in Works Out.
- This episode and "Flexes Its Muscles" are the basis for "Ralphie Strikes a Nerve", as they travel inside the human body (former) as they struggle to build a robot (latter)
- The white blood cells' would-be consumption of the Bus is a reference to Fantastic Voyage.
- Ralphie's last name is revealed when the Friz talks to Ralphie's mom when she answers the phone. His middle name is revealed in "Kids in Space". This makes Ralphie's full name Ralphie Alessandro Giuseppe Tennelli.
- This is the second episode to take a field trip inside a human body and the first episode to do so other than Arnold's which was first seen in For Lunch.
- Ralphie is the first of Ms. Frizzle's students to get sick. The second is Dorothy Ann in "Sees Stars"., and the third is Carlos in "Carlos Gets the Sneezes". However, Ralphie's illness is more prominent, as this episode is about the immune system and germs while "Sees Stars" is about stars, and it wasn't explained how Dorothy Ann was sick. In the latter episode, Carlos has an allergy to pollen and does not have an illness.
- This is the only episode in which the class (except for Ralphie and Liz) doesn't return to normal size at the end (not shown).
- This is the second time the bus shrinks, but the first where it shrinks with Arnold and without Ralphie or Liz.
- The William Tell Overture plays in one scene where Ralphie's medicine destroys the bacteria. This song also plays during "In the Haunted House" as the concerto for Carlos' invented instrument.
- The Ride of the Valkyries plays when the bus flies through Ralphie's window and into his bedroom.
- The song that plays while Arnold is whistling to himself is Ed Haley's "The Fountain in the Park", famously sung by Schmitt and Cernan on the Moon during the Apollo 17 mission.
- Kevin Zegers who would later voice Mikey is heard as one of the callers in the Producer Says.
- The FNN station is a parody of CNN.