You're crazy, Harry.
4 seconds sound clip from the An American Werewolf in London movie soundboard.
You can hear this line at 01:01:55 in the Blu-ray version of the movie.
Quote context
[...]
- Hey, let's go round the back.
- Why?
- Come on. We'll give Sean a scare.
- We're going to creep up round the stairs and give him a ripe old scare.
- Hey, did you hear something?
- Sean, those hooligans are in the park again.
[...]