(Rejected movie script)
The Yawn was a snake-based B.O.W. that resided in the Arkley Laboratory's greenhouse.
The Yawn was created by Umbrella by injecting the T-Virus into a common copperhead snake. The experiment was deemed a failure due to the creature's lack of heightened intelligence, only mutating to an unnatural size.
In the script, the Yawn was never defined by its true length, but George Romero did use numerous size references... Its body was six feet in diameter, jaws comparable to the open hood of a Cadillac SUV and teeth the size of windows (The standard height of a house window ranges from 24-60 inches).
In addition to size, the snake also had an increase in strength, able to crush a human in its jaws with minimal effort. It's power being comparable to a dozer-shovel. Although never referenced or shown, it was also likely to be highly venomous, as Copperhead snakes are also naturally venomous.
Sometime after its creation, the Yawn was deemed a failure to Umbrella as a B.O.W. for its lack of intelligence. Despite this, the creature was left to reside in the greenhouse alongside Plant 42 instead of euthanizing it.
Following the sudden death of Kenneth Sullivan and defeat of Plant 42, Richard Aiken lashed out at the dead plant in a fit of rage over the loss of his close friend. As he attacked the vines with his combat knife, Richard sliced a vine that oozed red blood... Tracing the "vine" up into the trees, he discovered a giant Copperhead snake coiled around the branches. Being struck from behind, Richard's torso was crushed by the creature's massive jaws before it swallowed him whole.
Chris Redfield, using a rope he looped over a ceiling beam, lassoed the snake to hold its head high enough to avoid further harm. Rebecca Chambers struggled to hold the rope as Chris sliced into the monster's stomach. Inside its stomach, he found a horribly mutilated but still alive Richard Aiken, who pleaded with Chris to kill him. As the snake struggled to free itself, the rope snapped. Without a moment to spare, Chris reached inside and pulled the pins on Richard's grenade belt before turning to run, the snake was killed in the resulting explosion.