Revealing mistake: In the scene were Mrs Doyle is listing the rude words and phrases used in one of Father Ted's favorite author's book's, she goes through all of them fine. Apart from the last one, when she says "Get your boll*cks out of my face" you can hear her laughing in the word "boll*cks" before she exits the room.
Revealing mistake: At the end when Ted flushes the toilet and kills the priest, we see an outside view of the priest and if you look at the bottom of his robes you can see a black square thing hanging down from the inside which must have been squirting the water out of his robes. Also to prove this, you are not able to see any water coming from the drain in the ground, which does not make any sense.
Revealing mistake: When Jack's wheelchair is at the top of the cliff and about to fall off, it's obviously a stuntman and not Frank Kelly sitting in it. Similarly, when the wheelchair falls, the dummy used isn't even dressed like Jack. (00:14:25)
Kicking Bishop Brennan up the Arse - S3-E6
Revealing mistake: In the bit where Bishop Brennan realises Ted did kick him up the arse, he runs up to Ted's house with his cape flying right out. The attachments holding up each side of the cape are visible.
Cigarettes and Alcohol and Rollerblading - S2-E8
Revealing mistake: When Ted jumps onto his bed (when the nun replaced their mattresses with bricks), you can see both beds are bouncy when Ted lands on his bed and Dougal lifts back the covers on the bed half way through the episode. (00:19:20)
Revealing mistake: When Henry Sellers jumps out of the window, it's apparent that it's pre-cut glass.
Revealing mistake: When Ted and Dougal are climbing the big rock after seeing St. Kevin's Stump, it's so obvious that a light is being shone on them from behind. They both have shadows even though it's a dark and cloudy day.
Chirpy Burpy Cheap Sheep - S3-E2
Revealing mistake: When Fargo brings Chris the sheep to Ted's place, Jack crashes down the stairs drunk and breaks all the poles of the banister. It's obvious all the poles have been pre-cut.
Chosen answer: It's characteristic of someone putting on a fake Irish accent.