Disclaimer: This is intended to be scary, gross, and disturbing. It may not succeed at being scary.
Even though she was spread eagled naked on the stone block in front of me her power was a tangible force in the room. Her distended belly spasmed from time to time. As the muscles contracted they reshaped her belly into an almost-cone shape.
Blood began to ooze from her birth canal. It was more than I expected. It flowed down to collect in a bowl hollowed into the rock she lay upon.
Next came the product of her womb.
It took some time to appear. It was black and sticky looking. Vaguely oblong, it writhed in an unexpected manner. Finally it came free and fell down to the floor where it flattened slightly before fracturing along multiple fault lines. Each piece dissolved into hundreds of black insects and spiders of every description. These rapidly made their exodus, skittering in all directions to disappear into the walls of the place.
My captor ignored these, choosing instead to focus on the blood that had been captured in the bowl. He was slight and small of stature and despite our current situation he continued his jovial manner, educating me. When I had agreed to be apprenticed to him I hadn't known about her. I had only seen the small power he had and wanted it.
Now he ladled the blood into a bowl which he carried over to the table on my right. "The blood is the life, you know." He commented gleefully. At the table he put the bowl down and then put a piece of bread into it and let the bread soak in, saturating it. "Of course, normally we make a witch's loaf by soaking bread in the urine of the possessed. But we don't want to transfer a demon today. No, today we are bringing forth something new." He smiled at me then, but it was not friendly.
The bread being sufficiently saturated he lifted it, dripping, from the bowl. He turned and fed it to her dog, her familiar I suppose, who ate it in one snap. The dog sat, and then lay down. It began to whimper and then went into a series of fits, each more violent than the last. My captor watched this in a fairly detached manner, standing next to her. She had collapsed after the birth and still appeared insensate.
The dog's paroxysms ceased and it stood and walked over to me. It reared up and placed its paws on my shoulders so that we were eye to eye. I remembered to struggle then, but I remained bound to the chair I sat in. I looked into the dog's eyes and saw intelligence there. But not the friendly, puzzled intelligence of a dog. In the soft brown eyes of this animal I saw myself as an insignificant means to an end.
The dog looked a moment longer and then leaned forward and licked me once, it's tongue parting my lips slightly. Then suddenly it forced my head back against unyielding stone and vomited down my throat. My eyes widened as it entered me and all is darkness since.