Continuity mistake: When Antinoos throws the bow to the ground after failing to string it, it lands tilting upwards. But by the time Odysseus picks it up, the bow is lying flat on the ground.
Audio problem: After the Cyclops finishes drinking wine, he throws the bowl back at Odysseus. In that shot you can hear the sound of it hitting him and falling to the ground. But the bowl doesn't actually hit him until the next shot.
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.