In the very last scene of the movie, and just before Blondie shoots the rope that is holding Tuco on the grave's cross. You can see a car moving in the background, screen right of Tuco's head. See more...
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The entry you are marking as a duplicate is:
|Title||The Good, the Bad and the Ugly|
|Original entry||When Tuco kills the fat man he is chained to whilst in the desert, in many shots this supposedly dead man can be seen breathing. Especially noticeable when he is on the tracks.|