"Likely cognitive manipulation. Hypno-patterns in the recording? Could be imbued warp energies. Many possibilities, hard to tell until I see it. Does not affect those with augmented brains though..."

Vael talks to himself, ignoring the ritual. Neither Hagar nor Geron were doing the Cult Mechanicus funerary rites anyway. Speaking of...

Vael examines the priest. Cognitive implants were rare and expensive. If the priest happens to have one, it should be extracted and its machine spirit preserved. And then passed on to his brethren or repurposed, it'll depend on the war conditions and Vael's mood.