Subliminal messages in the movies?

Were subliminal messages ever put in the films at the movies as an experiment to make people go to the consession stand? I have heard that years ago movie makers agreed to put a clip of a coke or popcorn in the main feature to subliminally cause folks to get thirsty or hungry for consession stand treats. Probably a UL but does anyone have any info on this particular rumour?

And yes, I did do several searches for this topic.

That’s funny. I only did one.