@Tersione @KeiosKod Looking at Sensei licking the floor in the last chapter, she's basically around a hallway corner from the three girls and Sumireko when she does it. I think that she just has to do it in a shadowed place and not specifically in a target's shadow. Just my perception, but it kind of fits with a black magic spell or curse.
Re-reading the last two chapters of this arc, Uname-sensei definitely acts like someone who was once the victim of bullying. She's wary, insecure, extremely focused on not making a misstep, eager to find someone to ally and feel solidarity with, very quick to apologize - pretty obvious stuff.