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This article is about the episode. You may be looking for the Buzz Book or the magazine story.

“It's a what'll?"
"A Diseasel, I think. There's a notice about them in our shed."
"Coughs and sneezles spread Diseasels."
"You had a cough in your smokebox yesterday. It's your fault the Diseasel came.
"It isn't!"
"It is!”
―Bill and Ben

The Diseasel is the twenty-first episode of the second series. It is based on the story of the same name from the Railway Series book Main Line Engines.


Bill and Ben are tank engine twins who work at a china clay quarry. Their jobs are to take the china clay in trucks along the main line for engines and ships.

One day, Bill and Ben arrange some trucks and leave to pick up more, but return to find them gone. Their drivers notice a patch of oil on the tracks and suspect that a diesel is responsible for taking the trucks. Mishearing this as "diseasel," the twins remember a notice in their shed saying "coughs and sneezles spread diseasels," and they argue over who is responsible. Their drivers intervene and make a plan to get the trucks back which involves removing the twins' nameplates and making them identical, as the diesel is unaware that they are twins.

The twins find the trucks in a yard, with a large green diesel at the front. Ben hides behind, with Bill going forward to demand the trucks back. The diesel claims the trucks are his and tries to shoo Bill away, but Bill reverses behind the trucks and Ben rides forward surprising the diesel (thinking it is the same engine). This continues for a while, causing the diesel to get dizzy. The twins then reveal themselves to him.

Edward arrives at the scene and asks what Bill and Ben are doing there. They claim that the diesel stole their trucks, but Edward scolds them for their rudeness. The twins apologise and the diesel forgives them. He introduces himself as BoCo and explains that he got his trucks mixed up with Bill and Ben's. Edward then sends the twins to take their lot back once they have picked up BoCo's trucks in exchange for theirs. After Bill and Ben leave, Edward tells BoCo that they do not mean any harm but can be maddening at times. BoCo laughs and replies that "maddening" is the word.




  • One barge has "Steve" written on it and a boat is labelled "Terrey." This could be a reference to crew members Stephen Asquith and Terence Permane.
  • A reference to the events were mentioned in the third series episode, Buzz, Buzz.
  • This episode marks with a few things:
  • This episode is one of the few instances in which every character who appears speaks.
  • In the restored version's long distance shot of the twins at the harbour, the track that sunk into the sea can still be seen facing downward.
  • The title is a portmanteau of the words disease and diesel.
  • The footage speeds up as Ben races through Wellsworth and as both twins play their trick.
  • This episode is titled "The Diesels" on the Roku Channel.
  • This episode was never released on VHS and DVD in South Korea.


  • One of the twins' drivers says, "We'll take away your names and numbers," but the twins were not given numbers in the television series. This is likely due to the script for the episode being taken verbatim from the original story.
  • In the restored version, two hands can be seen pulling Bill and Ben backwards with wire. Also, the exposed end of the set can be seen in a still from the episode.
  • When Bill comes up next to BoCo, studio equipment is visible on the right.
  • When Bill and Ben annoy BoCo, he is missing his eyebrows.
  • When the narrator says "Bill took his place," the track where Ben was previously bounces up.
  • When Edward arrives, his bogie is derailed.
  • When the twins apologise to BoCo, Edward disappears, indicating that the footage from where Bill was accusing BoCo of being a bully was used at that point.
  • During the scene where the twins are puffing backwards and forwards to trick BoCo, they both have Bill's whistle sound despite usually having different whistles.
  • In the shot showing Bill and Ben's cabs, a camera shadow is visible on one of them.
  • In the final shot, Edward's whistle is bent.
  • Throughout the episode, the studio is reflected in BoCo's windows.
  • When Bill and Ben puff through the level crossing and Wellsworth Station, studio equipment is seen at the top of the screen.
  • During the twins' trick, BoCo always looks at Ben whenever he comes and just stares ahead whenever Bill comes.
  • In the close-ups of BoCo looking angry in the restored version, there is greenery behind him rather than the yard.
  • In the UK dub, when the narrator says "The twins were abashed," it shows Ben smiling, even though the word "abashed" means "embarrassed" or "ashamed."


[Bill and Ben's drivers examine oil left at the scene of the crime]
Drivers: That's diesel.
Bill: It's a what'll?
Ben: A diseasel, I think. There's a notice about them in our shed.
Bill: Coughs and sneezles spread diseasels.
Ben: You had a cough in your smokebox yesterday. It's your fault that the Diseasel came.
Bill: It isn't!
Ben: It is!
Drivers: Stop arguing, you two. Let's go and rescue our trucks.
Narrator: Bill and Ben were horrified!
Bill and Ben: But the Diseasel will magic us away like the trucks!
Drivers: He won't magic us. We'll more likely magic him!

'Drivers: [about the suspected diesel] Listen, he doesn't know you're twins. So we'll take away your names and numbers and then this is what we'll do.

BoCo: [looks up at Bill] Do you mind?
Bill: Yes. I do. UK dub: I want my trucks, please. / US dub: I want my cars back.
BoCo: These are mine. Go away!
Narrator: UK dub: Bill pretended to be frightened. / US dub: Bill pretended not to be frightened.
Bill: You're a big bully! You'll be sorry!
Narrator: He ran back and hid behind the trucks on the other side. Ben now came forward.
Ben: Truck stealer!
Narrator: He ran away too. Bill took his place. (Bill and Ben proceed to taunt BoCo several times) This went on and on 'till the diesel's eyes nearly popped out.
BoCo: STOP! You're making me giddy. [Bill and Ben gaze at him] Are there two of you?
Bill and Ben: Yes, we're twins.
BoCo: I might have known it.

Edward: Bill and Ben, why are you playing here?
Bill: We're not playing.
Ben: We're rescuing our trucks. Even you don't take our trucks without asking, but this diseasel did.
Edward: There's no cause to be rude. This engine is a Metropolitan Vickers, diesel electric type 2.
Narrator: The twins were abashed.
Bill and Ben: We're sorry,
BoCo: Never mind. Call me BoCo. I'm sorry I didn't understand about the trucks.
Edward: That's all right then. Now off you go, Bill and Ben. Fetch BoCo's trucks, then you can take this lot. There's no real harm in them.
Edward: But they're maddening at times.
BoCo: [chuckles] Maddening... is the word.


In Other Languages

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Language Title
Brazilian Portuguese Edward, O Pacificador
Chinese Mandarin 生病了
Croatian Dizel Dolesti
Czech Diesel
Danish Bill og Ben og Vogntyven
Dutch De Viesel
Finnish Tautinen
French La Diesel-Grippe
German Dieselitis
Greek Τα βαγόνια χάθηκαν
Hungarian A Dízelmozdony
Italian Solo un Equivoco
Japanese ふたごのビルとベン
Korean 빌과 벤
Latin American Spanish Problemas de Mellizos
Norwegian Disyselen
Polish Choroba Diesel (Original)
Chorobowóz (Alternate)
Romanian Dieselul
Russian Простудизель
Serbian Dizizel
Slovenian Dizelska Lokomotiva
Swedish Disyselen
Turkish Dieselteri
Ukrainian Дизентиризиль
Welsh Bil a Ben

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  • Thomas and Friends Season 1-4