Morgana's Dagger

In the 5th episode of Series 3 Merlin is taken to the Crystal Cave to see the future where he sees Morgana brandishing a dagger and stabbing Uther. In reality Arthur gave this dagger to Morgana as a present for her birthday. That night Merlin tries to stop the future and causes Morgana to fall down a stone staircase and into a coma. While she is unconscious she hears Uther tell Gaius that he is Morgana's father. When she recovers she attempts to take revenge by stabbing Uther but is stopped in the nick of time by Merlin.