Plot hole: During the scene where Merida gives her speech on "breaking tradition", her mother, as a bear, moves silently behind the majority of the crowd, so they don't see her. Fair enough. However, Merida and her father's clan are all looking in the same general direction (towards the crowd) while she's speaking - how does no one from Merida's clan see a bear moving at the back of the room?
Continuity mistake: When Merida is climbing the rock to drink from the waterfall the rock is several meters away from the waterfall, but a few shots later it is centimeters away.
Continuity mistake: After Mor'du gets crushed by a large piece of stone, and as the sun is rising, Merida removed the tapestry from Angus to place over her mother, who is still a bear, in hope to break the spell. Angus also appears to be in the circle of stones, yet, in the shot that views everyone in the circle of stones from above, Angus is nowhere in sight. (01:33:00)
Continuity mistake: After Elinor saves Merida's bow from the fire, it is colored white while being slightly singed. However, when Merida uses the same bow later on, the bow is now dark brown, and the discs on it are gone.
Continuity mistake: The position of Merida and her brothers' thrones switch sides before and after their meal.
Answer: The stone circle is like a gateway to the spirit world, something slightly supernatural. Angus senses this, and it makes him freak out.
Ioreth