As Merlin handed Morgana the poisoned water, he felt sick. Guilt was racking through him, screaming at him to snatch the pouch back, to stop this course of action before it was too late. Not her, not Morgana, not his friend…
As Morgana threw Merlin through the air, knocking him unconscious as his head hit the ground, she felt the glee coursing through her. Finally, after all these years, he was in her grasp. Merlin, the backstabbing, meddling servant that had come between her and the throne for so long…
Morgana accepted the water skin thankfully, never doubting him, never thinking for one moment that he was doing this out of anything other than goodwill and friendship. Her trust in him was strong, her faith unwavering. She never saw it coming.
Merlin was already suspicious when Morgana attacked. Still, he wasn't aware of her presence, and it's hard to protect oneself from the unknown. He never saw it coming.
Merlin turned to see Morgana looking up at him, betrayal and disbelief swimming in her eyes. Her hand had gone to her throat, the throat that was now desperately working to draw in air that wouldn't come. Otherwise, she was alright; Merlin had, in a small and idle attempt to ease his guilt and lighten the horror Morgana was currently facing – horror that was shining so unbearably clearly through her eyes – used the most painless poison he knew about.
Morgana poured the poison into Merlin's mouth with an exhilarated smile. She was not going to make this easy for him; he who had betrayed her trust, foiled her plans, and killed her sister was undeserving of such mercy. No, Morgana would not make Merlin's passing an easy one, having specifically chosen the slowest, most excruciating poison she could find.
Staring down at his panicking friend, Merlin couldn't remember ever feeling this horrible in his entire life.
Morgana was thrilled just knowing of the horrors Merlin would soon be facing.
Merlin heard Morgana's anguished attempts to draw breath become louder, every failed bid more desperate, every high-pitched gasp somehow accusing him, and it broke his heart.
Morgana rose from Merlin's side. She knew she had things to do, that she couldn't stay any longer, but it was a shame. Merlin was so defenseless, so helpless, and it was her own hand that had caused this. Her heart sang at the thought.
Merlin gathered Morgana in his hands in a vain attempt to comfort her as she fought weakly.
Morgana kicked Merlin off a cliff.
Merlin cried.
Morgana left.