Idiomatic expressions

[Preminiser]

during an english lesson I came across a question that asks for the idiomatic expressions of the following:blood, sweat and fun.
flesh and brain.
I am confused, I can't find anything.
help.

[Casiopea]

The words fun and brains replace the words tears and bones:

Blood, sweat, and tears.
Flesh and bones.

All the best.