If he'd not been playing so thoroughly, Evan might have noted the approach of another creature. But neither his nose nor his ears picked up on the fact that somebody else was there, and he continued playing in the snow, oblivious.
Her laugh is what alerted him, making him flip over onto his belly, though keeping low to the ground. Since it was a laugh and not a shout, he was not tense, just surprised.
When he noted that it was Niks laughing at him, Evan let his tongue loll out of his mouth, and he wagged his tail happily at her. She looked pretty all dressed up like she was. Like a fairy princess.
Evan waited for her to approach, knowing that even Niks might be a little intimidated by his size.