"Sometimes familiars are kind of subtle? Those are budded-off witches that won't yield grief seeds if you kill them, they don't grow until they've eaten a few people and they can sometimes take a while to do that and could be subtle. Most puella magi don't even bother killing them because fighting costs magic and risks getting killed and you don't get your spiky little prize at the end. If I learn to teleport and clean other people's soul gems and we start trying to earnestly eradicate the species, maybe it'd be useful to have a way to find familiars when they're just chewing on one dude and the main symptom is that he quit showing up to work and keeps calling his sister and hanging up on her."