When purchasing the two liquids intended to kill Arthur, Morgana is told by the potion maker that the clear liquid is Valerian, the anesthetizer, while the yellow liquid is Henbane, the poison that must be delivered through the ear. Guinevere does the opposite, pouring the yellow liquid into Arthur's glass, and the clear liquid into his ear. Despite the mix-up the liquids still perform their intended duty. Later, when the potion maker is brought in for questioning, he says the opposite as well, identifying the yellow liquid as Valerian and the clear liquid as Henbane.
When Guinevere is fleeing from Sir Gawain in the woods, the hood of her blue robe switches from on her head to off her head and back again multiple times, with no time for her to have moved it.
Gaius helps Merlin escape prison by slipping him the aging potion. It does not explain how Merlin was able to change into his Emrys robe.