"You must not eat so fast!"
Translation:Nesmíš jíst tak rychle!
Same question, wouldn't that translate as "you can't"? And on the other hand, why isn't "nemusis" possible?
Yes, that would be "you cannot". No, "nemusis" is not possible, it means "you do not have to".
What is the difference between sníst and jíst? Are they not interchangeable here?
sníst is perfective, the complete action. You must eat you meal quickly. Musíš sníst své jídlo rychle.
This sentence totally mystifies me. In English this is a very common expression. But the word “mustn’t / must not” while eating is almost always used as a strong suggestion — meaning “shouldn’t / should not”. “You shouldn’t eat so fast.” My understanding of “nesmíš” means “not allowed”, as if it’s some sort of rule. Would “Nesmíš jíst tak rychle” be typically used as a strong suggestion, and if not, (1) In what situation would this Czech phrase be used; and (2) How would you say “You shouldn’t eat so fast”?