Terrifying tag for monsters- anything mechanical?

Hey all, quick question on the Terrifying tag.  It says it causes fear, but does that have any kind of mechanical effect on the PCs?  Within the fiction of course you can have horses bolt, peasants screaming, etc., but beyond telling the characters how scary it is, does is do anything like a -1 forward on direct attacks or anything like that? 

There's no inherent dice-or-stats-or-whatever related stuff but you could always do that kind of thing.

GM: You see the aurumvorax, the most terrifying fucking weaselmonster you've ever seen in your life.  It shrieks and rushes towards you.  You feel your breath catch in your throat and the cold chill of the weaselfear grasps at you.  What do you do?
Rowan: I stand my ground, I fear no rodent!
GM: Oh, do you, now?  Sounds like you're defying the weaselfear with sheer willpower.  Roll + WIS.

Playing In A Wicked Age is a good primer for stuff like this. You learn how to "push."

"The banshee wails; its screech shatters the stones of the corridor, splits your eardrums, turns your bowels to water. You foam at the mouth, your vision blurs, you collapse, screaming, the sound digging into your mind. You shit yourself. You go mad."

somewhere in there, they interrupt

"Whoa, whoa, wait. No. I get the fuck out of there."

"Oh yeah? What do you do?"

and then there's probably a move, as Adam says.

For terrifying, I like to push all the way into effects -- cross the line a bit and take control of them. Tell them they do stuff, like moaning in dread, shutting their eyes tight, hiding, running away, freezing in fear. If they don't like it (they won't like it) ask them what they want to do instead and defy danger.

John, are you drifting "Oh no you fucking don't, asshole" into DW? That's playing with advanced Fuckery turned up to 11.

Don't get me wrong, I'm totally on board.

Yeah, Harper knows what's up. +Terrifying shouldn't be a mechanical penalty or like "you run away for 1d4 rounds," it's more of a descriptive tag. Some players love roleplaying fear, insanity, etc, and they'll take that tag and run with it. Others don't like that sort of thing. If you need to force a little something on them, totally use those tactics to wrestle a little control and make them Defy Danger to face the beast. That's awesome.

yesss.  yes.

I love pushing "too hard" and making players say "wait, fuck off no way" but you can't always do that with new players.  There needs to be that pause (sometimes it's intentional, sometimes I just, you know, take a drink of water and look at them like "shall I go on?" and see what happens) with people you're not already familiar with or who see you as some "do not interrupt me" authority. 

Break them of that habit.