Just try and imagine what being a passenger on that plane must have been like.
In general Curtis' One-Winged Angel form, Body Horror abound, the eye itself seems to be made of cancerous tissue rather than what eyes are usually made of, His face rots off to a monstrous dog-like skull thing, and the right side of his chest seems to be comprised of solely lung as it contracts and expands disturbingly, at least William eventually ended up as something similarly horrifying but more... uniform.
The fact that adds on to this, this is the first time we actually can see the detail of a G-mutation, as well as the transformation itself, seeing as the last G-creature was rendered in limited PS1 graphics.
One of the things that makes it infinitely worse, the host of G is still conscious, Curtis briefly regains control, begging his Sister to run away, while he is doing this, he is holding back his clawed arm from stabbing her, while the eye in the shoulder goes nuts! heavily implying that the "mind" of the G-Virus is inside the eye.
