Obviously, when dealing with white shadows, you must take extreme care not to spook them! They are a sensitive sort, and you must never make eye contact with them! Fortunately for you, they had their head covered! White shadows do not speak English, they speak in the ancient tongue of the necromancer Locke.
You are very lucky to still be alive after an encounter like that! Normally, when a white shadow takes a victim, they enter through the nose and attack the brain. When they are done, they turn into a white powdery substance and drop the razor they used for the attack.