The Devils of the Devil tribe while innately chaotic and enthusiastic seekers of gore and pain infliction, did have organized structures and that was especially the case for the Devil Chief's Estate.
Hal and Sassy went invisible... he granted Sassy the ability so that she could walk by his side and keep an especially sharp eye on the surroundings as she planned to spring into attack at a moment's notice.
Sassy had her two dangers in hand but did not imbue them with her toxins or make use of her cultivation in any way as that would immediately deactivate her invisibility and ruin the whole point of being covert.
While invisible, they could still see each other but there was a kind of translucent feel to it that made it clear that the effect of the Invisibility was on.