I know this is not a movie to be taken seriously, but I find this fact curious.
Although people cannot perceive every movement the food does, so for them it would be like the movement of an inanimate object, under several circumstances they should have at least suspected that some weird thing is happening.
For example the scene where the honey jar suicides itself should have the one that bought it wonder how something that was on the bottom of the shopping cart could fell outside of it, similarly how a sausage can go to the sill of the window even though it wasn't absolutely near it, or how a single sausage is suddenly on a table.
I think there's no explanation for this on the movie but maybe some reason was later given by the creators.
Which is that reason, if it exists?