The scene you mention comes up for a bit of discussion each time we watch "Charlie Chan at Monte Carlo" during our Monday evening Chats! If you play it frame-by-frame, you can see that as the car is just about to come into contact with the person in question (not to give anything away to those who may not have seen the film, yet!) he...disappears. When audiences originally watched this picture in a theater, they could not, of course, have been able to re-watch it in the same manner as we can today. It happens so fast, that one just sees the car run him down.
Now, as for how this effect was created, perhaps the car was filmed rolling very slowly toward the "victim." As the car came very close, it stopped momentarily, he left the scene, and the car continued to roll on slowly. When it was all put together and played at a fast speed, it looked as if the car had run down the fleeing killer. As I recall, this particular clip lasts, at most, for just a second.
I hope that this helps, Jack. Thank you for bringing up this interesting tidbit!
