Wowee! Old horrible really said a frightful mouthful.
— Velma Dinkley (Nicole Jaffe)
4 seconds sound clip from Scooby-Doo, Where Are You! - What the Hex Going On (S1E6).
You can hear this line at 00:09:33.549 in the Blu-ray version of the episode.
Quote context
[...]
- That's just about as old as you can get.
- It sure would help if we could find another clue.
- Him.
- Ghost?
- Either the fortune is here by morning or all those in the Wetherby house shall grow old! Now go!
- Wowee! Old horrible really said a frightful mouthful.
- But we're not going to let that scare us.
- No, Shaggy. We're going to solve this mystery.
- Hey, where's Scooby? Uh-oh. I bet he's in that closet. Out to lunch.
- Yeah. With Scooby, I wouldn't be surprised.
- How do you like that? He didn't even invite me.
[...]