Despite Lewis being a dog with skeletal markings, he's always been afraid of many things. He is afraid of his own shadow, squirrels that may dart past his trail, and sometimes even just his tail brushing against his legs when he walks.
Sometimes he tries to face his fears. This is one of those times.
He braves the werewolf mask before him, the tattered clotting making him uneasy. He slips it all on, staring up at the glorious full moon. He gazes, awestruck in its beauty. He tells her how pretty she is, howling for her attention. He's not scared. He feels dumb with the costume on, realizing how stupid his fear of it was to begin with. But it fits the occasion, so he keeps it on.
As he stares at the moon.