In the early days of building humanoid automatons, the ability to construct an intelligent brain ultimately proved beyond the skill of Renaissance inventors. For this reason, many of the earliest robots ever built were entirely headless. They were not, however, thoughtless.
From outside, these androids appeared to be little more than suits of armor with their helmets removed. Inside, however, they were filled to the neckhole with a viscous, black fluid that sloshed around loudly as they moved about, and frequently leaked from their joints. This substance, referred to as “naphtha pudding,” is believed to have been an early, petroleum-based ferrofluid that served as an interface between the inner self and the world beyond.
The reason for this extremely vulnerable design, later dubbed “the dullahan configuration,” was that it removed the need for a brain by allowing automatons to borrow all of the necessary complexity for consciousness from their surroundings. Any sufficiently-detailed ambient environment could transform them from lifeless tubs of ooze into thinking, feeling beings, but forests tended to have the strongest effect. The complex, fractalline network of branches and limbs that surrounded them at any given moment served as an excellent substitute for the central nervous system that they lacked. The state of the forest also influenced their behavior: in summertime, they danced about like madmen; in winter, they paced back and forth in restless contemplation.
There were three significant problems with these androids that ultimately led to the end of their kind. The first was that they were fragile; in addition to the flammability of their perpetually exposed innards, whenever they would tip over (which was apparently often), their lifeblood would spill out all over the earth, killing them in seconds. Some were even built with umbrellas attached where a spine might have been to prevent rainfall from diluting them to death. The second was their inability to integrate with humanity; their composition required that they exist in seclusion from society, and their lack of sensation beyond touch and kinaesthetic awareness made any form of command by others impossible.
The third was that having an ambient brain was unreliable at best. There was no way for an observer to know exactly what dullahan-configured androids were thinking about as they fumbled their way through the wilderness, but it was clear that they spent the entirety of their brief existences lost and confused. Additionally, if two were ever found in close proximity, their bodies would attempt to share the surrounding brain, resulting in erratic behavior that inevitably led to the death of both.