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“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.


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 find a patch of oil on the ground and realise a diesel is responsible for taking the trucks. Mishearing this as "diseasel", the twins argue who is responsible stating that "coughs and sneezles spread diseasels". Their drivers, laughing, stop the twins from arguing and make a plan to get the trucks back which involves removing the twins nameplates and making them identical.

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 when Bill disappears 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 explain that the "dieseasel" 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 pick up BoCo's trucks in exchange for theirs.

After the two leave, Edward tells BoCo that Bill and Ben do not mean any harm but can be maddening at times. BoCo laughs and replies that "maddening" is the word.




  • This episode is based on the story of the same name from The Railway Series book, Main Line Engines.
  • In both the story from The Railway Series and the UK narration of the television series, Bill "pretended to be frightened" when he confronted BoCo. But in the US narration, Bill "pretended not to be frightened. 
  • 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.
  • This is the first time and only time until Journey Beyond Sodor where an engine's basis is mentioned.
  • BoCo's surprised face mask was only ever used in this episode.
  • The footage speeds up as Ben races through Wellsworth.


  • One of Bill and Ben's 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 nearly identical word-for-word to the original story.
  • In the restored version, two hands can be seen pulling Bill and Ben backwards with string. Also, the 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 a 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, there is greenery behind him, rather than the yard.


In Other Languages

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Language Title
Brazilian Portuguese O Diesel
Chinese 生病了
Croatian Dizel Dolesti
Czech Diesel
Danish Bill og Ben og Vogntyven
Dutch De Viesel
Finnish Tautinen
German Dieselitis
Hungarian A Dízelmozdony
Italian Solo un Equivoco
Japanese ふたごのビルとベン
Korean 빌과 벤
Norwegian Disyselen
Polish Chorobowóz
Romanian Dieselul
Russian Простудизель
Serbian Dizizel
Slovak Diesel
Slovenian Dizelska Lokomotiva
Spanish Problemas de Mellizos
Swedish Disyselen
Thai หัวรถจักรแฝดใหม่คู่ที่สอง
Ukrainian Дизентиризиль

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