It's an Italian idiom also, which kind of figures.
It surprises me that the French don't have such slang, because it's so obvious when you cut into a nice, fresh round of stinky cheese. Sometimes, you even get a sound-effect as trapped gasses are released. Plus, it just seems French to me - French-style humor.
Isn't it true that "un petit petard" is French slang for "fart"?
(A "petard" is a bomb that you hang on a wall to blow a hole through it and gain access to fortifications. Often, the bomb crew was killed in the blast, thus the English expression "being hoist by one's own petard".)
in the sentence "il est facile de couper ce fromage", "il est" is impersonal, like a set formula: 'il est facile de' + infinitive.
if you want "il" to represent the cheese, you need to say: "il est facile à couper, ce fromage", which is an emphatic form of "ce fromage est facile à couper". The preposition "à" is only attached to facile: ..."facile à" + infinitive
Maybe you have noticed that the preposition changes when you move from a real subject (le fromage) to an impersonal subject (il or c'):
- (the) cheese is easy to cut = le fromage est facile à couper
- it is easy to cut (the) cheese = il est/c'est facile de couper le fromage.
Of course, both mean the same thing at the end of the day.
Not really. It is one of the hardest things to learn and you just have to memorize: "Il veut couper le fromage" "Il apprend à couper le fromage" "Il oublie de couper le fromage" "Il aime couper le fromage" "Il hésite à couper le fromage" "Il s'occupe de couper le fromage" "Il promit à sa mère de couper le fromage" "Il enseigne à sa mère à couper le fromage" "Il pense couper le fromage" "Il songe à couper le fromage" etc.