Cinemas' in this country used to put in what was then called 'spoilers'. It was a subliminal one frame shot injected into the film, not visible by the naked eye, but taken in by the sub-conscience part of the brain. 'Spoilers' would generally be that of drinks or food, so when the intermission came, cinema go-oers would automatically want to have something to eat or drink to satisfy their craving (little realising it was the spoiler that triggered this of). So sales of refreshments were pretty high. I cannot remember (date) when this was outlawed, and cinemas' banned from this practice.