Named Yawn because of the way it held it's mouth wide open before it attacked, it was the result of
t-Virus experiments on an adder. Umbrella scientists attempted to keep it under control, but because of the outbreak, it broke out of containment and caused havoc throughout the
Spencer Mansion, likely killing many in the process.
On top of it being extremely venomous and dangerous, it grew extremely large, but still retained agility. Also, It's venom was so powerful that it could only be cured with a special serum, which supplies of were kept in the Mansion. Once taken, the user would be immune to the venom's effects permanently. If the person bitten was not cured, they would die.
S.T.A.R.S. Bravo Team members
Rebecca Chambers and
Richard Aiken were attacked by Yawn, with Richard taking a venomous bite in order to protect Rebecca. Later, Alpha Team members
Jill Valentine and
Chris Redfield encountered it and eventually defeat it.
In all appearances, Yawn is battled in the Library. However, in Resident Evil Deadly Silence, another more resilient Yawn can be found in the location where
Plant 42 was. The serum can be found in 1F Chemical Storage Room.
A
Snake-like creature was later developed by Neo Umbrella which was named
Iluzija and based on a C-Virus infection on a human host.
