What conceivable motive do you think we possibly could've had?
3 seconds sound clip from the Dead of Night (1945) movie soundboard.
You can hear this line at 00:18:29.220 in the Blu-ray version of the movie.
Quote context
[...]
- You seriously think we cooked the whole thing up between us?
- Well, as an explanation, it's not any more far-fetched than Mr. Craig's.
- And the jokes on me, too, for I didn't know anything about it.
- A funny sort of practical joke. It isn't funny.
- What conceivable motive do you think we possibly could've had?
- No doubt you thought it would be very amusing to watch my cherished disbeliefs being shattered.
- Very clever of us, I must say. I wonder if we have any more surprises up our sleeves?
- Then, Foley, you say something, something about the death of a man I've never heard of.
- And that's where my dream becomes a nightmare, a nightmare of horror.
[...]

 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)