humblegunner, Notice the body difference? The chunky body of the Cottonmouth on the bottom. Look at the tail also. See how the bottom one is blunt and goes down real quick? The bottom snake is the same body diameter but much shorter in length.
Not only that, but HG’s snake was downright blue where I’ve never seen a blue water mocassin/cottonmouth, they’re usually greyish with some yellow scales, or even a diamond-back type pattern, not solid-colored.