Something I noticed about Hemalurgy while reading through Mistborn: The Final Empire again.
On page 540-541 the book states . . .
Kelsier stumbled into the room.Vin followed, but she knew
what she’d see. The corpse lay near the center of the chamber,
flayed and dismembered, the head completely crushed. It was
barely recognizable as human. The walls were sprayed red.
Now, we know this was where Marsh was supposed to meet Kelsier, and that the Inquisitors got to Marsh and "recruited" him. Could it be that this corpse was the sacrifice used for Marsh? There was a lot of blood involved in this death, and the skull was crushed like what I'd assume would happen when one had two steel spikes driven through you into someone beneath you. The dismembering could have included the skull, perhaps, as a spike was driven through your spine. . .
The point of this is, I think when making an inquisitor, the spikes have to go through the sacrifice in the same spot as in the Inquisitor. So the brass spike of an inquisitor goes through the heart, another spike (I think it's steel) goes through the spine, and two steel spikes go through the eyes. Also, there's no spike in the stomach. Kell punched the Inquisitor there during his fight, and he would have felt the metal.