Screamer

The Screamer was a special infected in the early stages of game development, preceeding The Witch and The Boomer's puking attack. The idea of the Screamer was for it to lurk, much like the Witch, in different areas, paying no attention to it's surroundings until coming in contact with a Survivor. At this point, it would sound a warning, like the witch. If agitated enough, it would not attack, as it is bound in a straightjacket, but run off screaming, attracting a horde, like the Boomer's bile.

At this point in development, all the Boomer did was explode when killed, splash damaging nearby survivors. When the Screamer was cut, the Boomer got it's bile attack and new death.