Can anyone please explain what the hell happened in the film Banshee Chapter? Obviously spoilers.

OK so the military/CIA are using the condensed fluid of brains from corpses to help channel communication with unknown entities via the use of MK Ultra, at least that's how it's conveyed across in the movie. However what I don't understand is this.

At the end we discover that the signals are coming from a military lab in the desert and the main source is a creature that is submerged in a tank, full of the black fluid. What is the creature supposed to be exactly?

The creatures shown in the movie pursue anyone hearing these signals for an unknown reason and leaves more questions then answers. And not in a good way.