The music that an ice cream van plays is essentially never-ending. Its design means that the music can only exist as a continuous loop (the music can be stopped and started but if left to play then the end of the music will always revert back to the beginning just like a wind-up music box). This never-ending cycle of music is used to announce the arrival of a short lived piece of food, ice cream. The ice cream is quite different to the music that represents it as it has a definite ending (once eaten) and if left alone it’ll eventually melt and cease to be all by itself.
In a parallel universe these contrasting experiences would be reversed.
There would be an ice cream that existed that once made never melts or goes off. These never ending ice creams would always be available for tasting and would always retain their flavour whether being tasted or not (just like the ice cream van music always exists whether being played or not). When this never ending ice cream is tasted by someone a piece of music appears in their head. When this happens you have two options, either you can accept the delivery of the short piece of music into your head and listen to it which, once heard, can never be heard again; or, you ignore the piece of music in your head and just leave it there (this would be similar to the experience of having a piece of catchy music stuck in your head – it’s in the back of your mind but you’re not paying much attention to it). If the music is ignored and left to be, it will slowly dissolve into nothingness just like the melting ice cream.