Rain noticed a particular aspect of the ice dragons' movements that struck him as unusual. Typically, in the aftermath of a large battle or conflict, creatures might flee en masse and travel much farther away from the site of the confrontation to seek safety or avoid further conflict until they can regroup.
However, in this instance, the ice dragons' behavior didn't align with this expected pattern. Instead of scattering in a disorganized manner or fleeing far south, they seemed to be moving in a more organized and methodical fashion. They didn't travel as far as one might anticipate after such a battle. This behavior made Rain question their motivations and actions.