Yellow tails of juvenile Cottonmouths and Copperheads
Juvenile Cottonmouths and Copperheads have bright, sulfur yellow-colored tails that they use as a lure to attract prey. Young juveniles hold the tail upright (vertical) and wiggle the yellow tip like a caterpillar to lure small prey within striking distance.
A young Cottonmouth with a yellow tail
As the Cottonmouth grows older the tail darkens to black
Juvenile Pigmy Rattlesnakes also have yellow tails