I'll go first. Don't follow until I give you a sign.
6 seconds sound clip from the Harry Potter and the Sorcerer's Stone movie soundboard.
You can hear this line at 02:02:11 in the Blu-ray version of the movie.
Quote context
[...]
- Wait a minute. He's... snoring.
- Snape's already been here. He's put a spell on the harp.
- What?
- Come on!
- I'll go first. Don't follow until I give you a sign.
- If something bad happens, get yourselves out.
- Does it seem a bit quiet to you?
- The harp. It's stopped playing.
- Jump!
[...]