Continuity mistake: When Odysseus is telling Calypso about his scar, he rises from the water. In one shot his head is down and his arm is lowered. In the next, his head is up and his arm is raised.
Continuity mistake: The blood on the face of the little boy at Troy changes constantly throughout the many shots of him.
Continuity mistake: When the Trojan Horse was being inspected by King Priam and his men for the first time, why didn't he see the Greek soldiers hiding inside? There were plenty of large gaps between the planks used to construct the horse.
Answer: The Trojan War itself was a decade long, followed by Odysseus' ten-year journey home to Ithaca, so all told he was gone roughly twenty years.