For Freddy, it's an exciting prospect, meeting someone new, and he always perks up at the sight or sound of someone he's not yet met actually returning a greeting. Perks rather than brightens, mind, because to say that he brightens would be akin to an already cloudless sky somehow becoming more clear or, alternately, the sun going supernova. As such, his expression is reminiscent of an absolutely delighted puppy when he catches a young stranger waving back.
Having no particular goal in mind for this outing, the wave naturally becomes an invitation, whether it was intended as such or not, and Freddy beelines for its origin, his only offered warning an enthusiastic, "Hello!" The word gives his target about a heartbeat's chance of escape, good only to those with the reflexes of a rabbit or, more likely, a ninja. Barring which skill, his prey is quite easily caught beneath the gentle paws of his presence.