I came across the phrase “His cheeks reddened as he curled up his fingers” in the scene, a six-year-old Ruthenian boy, Lubji Hoch, who later becomes one of the world’s most powerful media moguls, tries to buy an expensive brooch for his mother with small changes at a jewelry shop in Jeffery Archer’s novel, “The Fourth Estate”- P.35:
“The old man didn’t laugh, but gently explained to Lubji that he would need many more coins than that before he could hope to purchase the brooch. Lubji’s cheeks reddened as he curled up his fingers and quickly turned to leave.
What does it mean to “curl up one’s fingers”? I curl in (or inward) my fingers to sqeeze my hand, but I don't think I can curl up my fingers backward without being forced?
Is “curl up one’s fingers” an idiom or cliché to describe special emotions such as an extreme tension or embarrassment, or just a plain description of a bodily reaction?