Part 2/8:
To understand why Jacken was interested in Arya, it is essential to consider the context in which they met. Jacken's arrival in the Knight's Watch Caravan happens at a crucial moment; he is already confined and preparing for a journey north before Arya is smuggled into the group. Despite this, he seems to linger due to his intrigue with Arya, suggesting that she piqued his interest long before their direct interactions.
When Arya is disguised as a boy, her small changes in appearance might fool everyday observers, but not someone as trained as Jacken. His keen eyes would quickly identify the inconsistencies in her disguise—most notably, her expensive sword, combat stance, and her evasive behavior about her true identity.