Teen Wolf, Season 5

[Deaton, Stiles, and Scott are at the animal clinic, where Deaton has just pulled out a stack of old Polaroid photos, all of which depict various supernatural creatures with bloody holes drilled into their heads]

Deaton:
What I'm about to show you isn't supposed to exist. This is the only surviving evidence of Dr. Valack's time as Chief Medical Officer at Eichen House. To call it human experimentation would be... charitable.

[Stiles' eyes widen at a photo of a woman who is painfully covering her ears with her hands]

Deaton:
A Banshee. She died screaming.

Stiles:
So, he drilled holes into their heads? All of them?

Deaton:
That was the experimentation part. He did it to werewolves, Banshees, wendigos... any creature he could get his hands on. And Valack found that trephination would initially heighten their powers, but to levels that couldn't be contained.

Scott:
So, he wants to make Lydia more powerful.

Stiles:
Yeah, except she's going to end up like them.

Deaton:
Worse, actually. Lydia's abilities were already pretty exceptional to begin with. Putting a hole in her head will be like causing a leak in a nuclear reactor. She'll hear everything-- every death, every dying scream, all at once.

Scott:
[worriedly] That's gonna kill her.

Deaton:
Not only that... Her own dying scream could be so powerful that it might kill everyone around her.