Vacuum
"Speak again," Driola encouraged.
"Huh?" Erdeta answered, and that dry response, still managed to scare at least ten ghosts away!
That was the physical example. The auditory example, however, was that the ghosts stopped 'booing' when they were spooked. They were just silent and floated away.
"They're silent every time I talk," She muttered, and then started walking towards the enemies. "You're scared of me, huh? Boo! Hahahahaha!"
It wasn't like her to scream this much, so this was an odd scene even for her friends who knew her well. They were confused and felt uneasy, on top of that, they were also pondering over the realization that they wouldn't die here because their friend was paving a safe route for them.
Truly there was a lot to process! They were useless in this situation too, as they couldn't fight the ghosts. This felt like a kick in the shins…