(Fuufu genka wa inu mo kuwanu;
“Even a dog doesn’t eat a husband-wife fight”)
Fights between marital partners are based on small issues that seem ridiculous to outsiders but can become emotionally charged. Then they quickly blow over and the couple returns to its prior equilibrium. It’s best not to get involved. The image of a dog illustrates the not-getting-involved portion: dogs will eat just about anything, but won’t even be interested in this.
The first four characters form a single compound noun. 夫 (here, fuu) is “husband” or “man” while 婦 (fu) is “bride” or “woman,” and logically enough, 夫婦 means a husband-and-wife pair. Both 喧 and 嘩 mean “noisy” on their own, but together as kenka they mean an argument or fight.
So all together, they make “husband-wife fight.” This noun is marked with は (wa) as the topic of the sentence, and then we get a little subject-verb pair that elaborates on the topic. The subject is 犬 (inu), “dog,” and the verb is 食う (kuu), “to eat,” in imperfective form so that it can take on a negative suffix. Interestingly, the suffix itself is in prenominal form, implying that either the phrase is meant to be attached to something else rather than used in isolation, or some odd grammatical quirk is forcing the shift. (It happens sometimes….) Or it’s a quirk on the part of the speaker? (See below.) Anyway, inu is modified by the particle も (mo), an intensifier meaning “also,” or in this case “even.”
The archaic and possibly odd grammar at the end may be replaced with the modern negative form, 食わない (kuwanai) without significant change in meaning.
A longer version of the saying adds と夏の餅 (to natsu no mochi), “and summer rice cake,” after 夫婦喧嘩, as a concrete example of something else dogs don’t eat.
This phrase comes from the famous playwright Chikamatsu Monzaemon, who used it in a joururi piece titled 淀鯉出世瀧徳 (Yodoigoi shusse no takinobori).
(“Fuufu genka wa inu mo kuwanedo oya genka hodo osoroshiki mono araji ka na.”)
[“Even a dog won’t pay attention to a couple fighting… but man, there’s nothing as frightening as your parents fighting.”]
(I took the liberty of trying my hand at classical grammar here, but didn’t bother trying to reflect that in the translation!)