Nope. Leave it closed.
5 seconds sound clip from the Mister Ed movie soundboard.
You can hear this line at 00:20:00 in the DVD version of the movie.
Quote context
[...]
- You know, I'm very flattered that I'm the only human being that you picked on to talk to, old horse.
- Uh, can I get you some oats or anything, old horse?
- Uh, can I open the window for you, Mister Ed?
- What?
[...]