Sam faltered for a split second at the sight of the snake, more from surprise than fear, though the yellow eyes were a haunting reminder of the yellow-eyed demon, and made his gut twist. He had a split second flash of a burning house, a shadowy figure with yellow eyes disappearing into the smoke, and knew that the other man had seen it.
It was a good thing that he'd already been imagining the light wrapping around the magic, because that made it easier to find the tendrils of it, set them ablaze with the fire from the memory, and lash out at the snake like whips, trying to curl around it and restrain it by the throat and tail.
But the visualization of the flames hurt, reminding him of hellfire. A furrow appeared on his brow as he envisioned a surge of water, coming up from somewhere deep inside him, flooding his mind and extinguishing the flames. He didn't release his hold on the snake, but held it down as water surged over its head, intending to drown it-- though even as he did, he realized that the idea of drowning an imaginary magical snake was a little ludicrous. It probably didn't need air to breathe.