The Whisper

In Blood Omen 2, Umah reminded Kain of the Whisper, a natural ability Nosgothic vampires had to communicate telepathically. This could be used in close proximity to guard their secrecy, or over long distances. Throughout the Legacy of Kain series, Raziel never once mentioned the Whisper, so it's possible that Kain's offspring missed out on this particular skill, despite it seeming pretty standard for Vorador's descendants.

Umah and Vorador used the Whisper to speak with Kain while he was travelling alone through Meridian and beyond. They offered advice and direction, helping him to progress, or find the Cabal contacts that held the information he required.

FURTHER OBSERVATIONS

In the Playstation version of Blood Omen 2, Kain and Umah had a white aura when we saw them using the Whisper. This effect was not present in the PC version.