twardy orzech do zgryzienia*
* a hard nut to bite
An expression used to say that something's not easy, hard to solve or to understand
"Jego choroba to twardy orzech do zgryzienia. Nie wiem, co mu jest."
"His disease is a hard nut to bite. I don't know what's wrong with him."
Submitted August 2020
Confirmed by 2 people