He can't be certain what he saw, but it was definitely an animal of some sort. The scratching at the panes of glass only confirms his suspicions. Chances are fairly low in this place that it was something harmless like a squirrel (god, wouldn't that just be the dream), so Crozier sets the buckets back down and grabs the rifle he keeps by the door for this exact reason.

By the time he yanks the door open he fully expects that the animal's down by the treeline or hovering in the bushes, and his surprise nearly makes him jump right out of his skin.

A wolf! What the hell!

Not worth the fight, not at all, so he slams the door in the wolf's face before it decides to invite itself inside.