Possible magic reveal? Reasons to believe so:
- Merlin wears the same clothes as in the shot with him and Arthur (blue scarf, red shirt) and the same counts for Arthur (red shirt). This says the scene is with the two of them, and not a manipulative trick of the editors.
- Big zoom in going on in the shot with Arthur. His eyes are spread wide (in disbelief/disgust?) and he lowers his head a little bit (at the very end), probably to watch what Merlin is doing since it looks like the action happens on the ground. Just look at his face expression: what is going on there?
- Same surroundings. All the walls are made of stones. Wooden doors.
- The ground Merlin puts his fingers on looks ”hard and brown” at first (before he touches it), like in the shot with Arthur and Merlin together.
- Another shot features 2 sticks slamming Merlin to a door and Arthur turning around hastily. This could mean there are enemies that need to be defeated and there’s no other way than using magic.
Whatever may be it, one thing is for certain: this scene will be big!