For example: My mother and I are like chalk and cheese.To eat chalk would be quite a different matter than eating cheese. Chalk is dry, powdery, pasty, tasteless, inedible. Cheese, on the other hand (especially good cheese), is rich, buttery, creamy, densely-flavoured and a pleasure for the palate. One you want to immediately spit out, the other you can't get enough of.
There you have it... The cheese expression for the day.