The priest is given chance to say final words. He pleads to the Lord for another chance to redeem his sins. The guillotine gets stuck as it is falling down. Under the law, the sentence is repealed and the priest is reprieved. They examine the guillotine and find nothing wrong.
Then it comes to the thief's turn and he begs to be spared. The guillotine gets stuck again and he is releasd. The guillotine is checked again and certified functional.
Then the engineer is asked to say his final words. He inspects the guillotine and says "I think I know the problem".