Oh, perhaps we'd better take off our costumes so as not to frighten him.
6 seconds sound clip from the Boo to You Too! Winnie the Pooh movie soundboard.
You can hear this line at 00:15:23.014 in the Blu-ray version of the movie.
Quote context
[...]
- We're on our way to Piglet's to have a Hallo-Wasn't. If you'd like to join us...
- Hoo! What are you waitin' for? Come on!
- Someone's coming! Ohh! It's a three-headed, bug-eyed, saw-toothed spookable!
- Oh, perhaps we'd better take off our costumes so as not to frighten him.
- Don't you know what this means? He's been pig-napped by spookables! Aaaaah!
- Hup, two, three, four. Hup...
- Pooh wasn't at Eeyore's either. And neither was Eeyore. And no one was at Tigger's.
[...]