The reflective motion was familiar in the way that Arya almost always hand a hand near her hilt too, so she was a young warrior. "They are," Sansa appreciated people who could see that before they saw the danger, "You could touch them, if you wanted." Summer and Shaggy Dog were likely the best for people to meet first.
Grey Wind was exceptionally wary, and Sansa understood that, knowing what happened to him, just as Ghost was cautious. Summer and Shaggy Dog seemed to embody Bran and Rickon better, both of them more trusting to begin with. "The black one is Shaggy Dog, the tan one is Summer."