Players who have not completed While Guthix Sleeps will still see Lucien in his Mahjarrat form despite not seeing it before the quest. According to Mod Seven, "People who have never met him have his image transferred into their minds by those that have by, erm, magic and wizards."
When a player talks in public chat while using this emote, the chat will appear near their feet, not above their head.
You can't perform the emote in front of a bonfire, even though it is a walk-able tile.
If you perform this emote while facing someone, it would look like Lucien was biting on their head.