Bogus "tractor beam" video

Museum of Hoaxes found this video that purports to show an audio speaker that pulls objects towards it.

Picture 2-90
Obviously it's fake. Audio speakers will not create a gravity field. But I'm not sure how they created the special effect. (Not that I know much about creating video effects.)

Perhaps they used some kind of fancy editing software. Or perhaps they did it a really low-tech way — moving the objects one frame at a time to make it appear as if they were sliding towards the speaker. If they did it the latter way, they managed to make the sliding effect look very smooth.

How do you think it was done?

Link