Continuity mistake: When the men enter the cyclops' cave, Odysseus crouches down and says "They keep sheep in this cave with them". Between shots his arm goes from being at a 90 degree angle to being at a 45 degree angle.
Continuity mistake: When Elpenor says "We will not reach Ithaca without you" Odysseus replies "Yes you will" and hugs him. In that shot Odysseus' right hand is on Elpenor's back, but in the next as Odysseus says "It is I who am lost" his hand is on Elpenor's head.
Continuity mistake: When Telemachus is born and Penelope and Odysseus hold him, Penelope's hand goes from touching the baby's arm to touching his head.
Continuity mistake: During the start of the battle in Odysseus's throne room at the end of the film, watch as the evil suitor hurls an axe at Odysseus and Telemachus, shouting "A river of blood!" Both duck as the axe flies towards them. Then in the very next shot, they duck a second time as the axe smashes into the wooden throne behind.
Visible crew/equipment: During the Trojan War, when Odysseus yells "Fight. Fight. FIGHT. ", a soldier plays the flute and they all run down the hill, a cameraman with a blue t-shirt and sunglasses is visible.
Revealing mistake: When the monkey points up the hill and Odysseus keeps climbing, modern houses and roads are visible on the ground below.
Continuity mistake: After Circe tells Odysseus that he must go to the underworld, Odysseus sits down on the bed and puts his hand on his lap. In the next shot, as Circe says "You are right to be afraid", Odysseus' hand is on the bed.
Continuity mistake: When Odysseus looks back at his men before entering the underworld, the men are shown in different places on the ships between shots.
Continuity mistake: When Odysseus holds up the bowl of wine and says "It's the drink of the gods", the bowl is grey. When he gives it to the cyclops it is brown. When the cyclops throws it back at him, it is grey again.
Continuity mistake: When Odysseus finds the little boy standing next to the ladder during the Trojan war, the angle of the sticks leaning against the ladder differ in the closeups.
Continuity mistake: A very blatant mistake in the Scylla scene. In one shot it is totally dark, with no light coming from the ship. In the next shot, Odysseus orders Anticlus to light a torch- and suddenly there is a ball of fire from which the soldier lights the torch.
Continuity mistake: When Odysseus surfaces from the water and grabs the mast, the shape of the mast and the ropes around it have changed from the previous shot.
Audio problem: When Tiresias describes Scylla to Odysseus he states, "She lurks in the shadows, hoping to fill her belly." However, when he says, "hoping to fill her belly," his lips don't match what he is saying.
Revealing mistake: During the battle at Troy, when Odysseus and Achilles are standing together surrounded by Trojan warriors, Odysseus lashes out with his sword and kills a warrior (just before Hector appears and challenges Achilles). If you look carefully you'll see that Odysseus merely swung his sword for show; it didn't connect with the Trojan warrior who fell dead.
Continuity mistake: When Odysseus carries Penelope into Eumaues' cottage, the position of Penelope's hand on Odysseus' shoulder changes between shots.
Continuity mistake: After the suitors throw Penelope's tapestry into the fire the position of the tapestry changes between shots.
Revealing mistake: The gaps between the boards of the Trojan horse are much wider in the inside than on the outside. This reveals that the soldiers are not really inside the horse, but on a set.
Continuity mistake: When Odysseus talks to Athena on his ship, the blanket on his shoulder pad constantly moves closer and further away from his neck.
Continuity mistake: When Circe tells her maids to make wine with honey, she turns around to look at them twice.
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.