Brain Form

Summary
The rarest Flood type is the brain form.

A brain form is a type of Flood unlike all the others because it lacks any sort of mobility. While the infection, combat, and carrier forms are dangerous and always hostile, the brain form is passive in a tactical sense. When the Flood attempt to control a starship or interface with a computer system, the brain form is used.

It normally contains the body of someone who has knowledge of the computer systems necessary for operation. Like the combat form, it can read the thoughts and memories of its host provided he or she is still alive, and it will sift through every memory until it finds what it needs. If it cannot find the information it requires, it will direct other Flood to bring it a new body to search while it consumes the last body.

It interfaces with computers the same way an Infection Form infects a host, through tendrils that attach themselves to the computer's "neural" system.

Images
http://img79.exs.cx/img79/4970/tbkeyesblob5dl.jpg