Literally, it says: bitter tears, salty tears.
That's what English terms idiom or idiomatic expression.
An idiom is a phrase that does not mean literally but has
a figurative meaning. That's just an expression that is
a symbol for something.
Kua muag ab kua muag dlaw is usually used in
the plural sense and means something like hardships
or difficulties.
In "Nraug Ntsuag hab Ntxawm Qaum Ntuj", after having been praised
for rescuing Heaven's Princess, her dad--the Heavenly King--asked
if the hero would take a field of cows and buffaloes as appreciation gifts.
He declined all and said those were just
kua muag ab kua muag dlaw haud
Nplaj Teb xwb. (Nor did he accept jars of gold and silver; he chose
the King's featherless chicken only. He took the Princess's advice on this
after their walks around the Heavenly Palace...I would have asked for her hands instead,
right?
)
