Humans that have befallen to an unknown ailment, causing black goo to spew out of their facial orifices. They seem to be trapped in the last few moments of conscious thought, repeating the same few seconds over and over. As they are humans, and do not pose an active threat, you shouldn't be shooting at them, Agent.
Finding out what the disease is and does, how it transmits, and how to cure it wil be critial to XCOM's overall goals.
In reports visible (and in the process of being censored) in the ending cinematics, it's stated that the "oil" seeping from their orifaces are ferrofluids, and are the same substance as the Silacoids (iron, silacon...): one Sleepwalker even vomits up a Silacoid in the Dam. It also says that the substance is actively re-writing their DNA, and during one Operation, one of your agents will wonder aloud if the Outsiders you are fighting may have once been human...