- Yes, but how did the dummy get from one room to another? Under its own steam? 
- Without knowing what he was doing, Frere took it himself. Impelled by the dominating Hugo half of his mind.
11 seconds sound clip from the Dead of Night (1945) movie soundboard.
You can hear this line at 01:36:25.430 in the Blu-ray version of the movie.
Quote context
[...]
- Say, you remember me. The name is Kee, Sylvester Kee.
- Why, hello, Sylvester. I've been waiting for you.
- You mean that half the time Frere was Frere and the other half he was his dummy?
- Exactly.
- And in the end, the dummy got the upper hand entirely.
- Yes, but how did the dummy get from one room to another? Under its own steam?
- That is the scientific explanation. But, no doubt, you people would prefer a more colourful one.
- That Hugo had become endowed with an existence of his own.
- Drink? Oh, I'm awfully sorry.
- Blimey, George is dying on us.
- There's nothing to be afraid of. We're your friends.
[...]

 Dead of Night (1945)
 Dead of Night (1945)  Phantom of the Opera (1943)
 Phantom of the Opera (1943)  Scooby-Doo, Where Are You! (1969)
 Scooby-Doo, Where Are You! (1969)  Halloween III: Season of the Witch (1982)
 Halloween III: Season of the Witch (1982)  Knight Rider (1982)
 Knight Rider (1982)