(In other news, water is wet.)

犬が西向きゃ尾は東
(Inu ga nishi mukya o wa higashi; “If a dog faces west, its tail points east.”)

Definition:

Self-evident. Blatantly matter-of-fact. Something is so obvious that it’s barely worth mentioning. Since a dog’s tail is on the opposite end of its body from the face, if the dog faces one direction, then yes of course its tail points in the opposite direction, thank you very much.

Breakdown:

We begin with the noun 犬 (inu, “dog”). It is marked as the subject of a verb by the particle が (ga). Next, though, we get another noun: 西 (nishi, “west”). This is the direction of the following verb, so grammatically we might expected nishi to be marked with (non-motion) directional particle に (ni), but here the particle is elided and unnecessary. After this we come to the verb: 向く (muku, “to face/turn toward”). It’s actually in conditional form and would properly be 向けば (mukeba), but has been compacted into a more slangy form.

The second half of the phrase is very compact. We have two nouns: 尾 (o, “tail”) and 東 (higashi, “east”), joined by the particle は (wa). The structure is parallel to 犬が西 in the first half: the particle has changed because we’re looking at a parallel repetition, becoming wa to emphasize the contrast between “the dog (overall) faces west” and “the tail points east.” And because the parallel structure renders it unnecessary, we find the verb elided entirely.

Notes:

There doesn’t seem to be anything particularly striking about this one. But then again, perhaps it should be self-evident?

Example sentence:

「空が曇ってても、朝は来るよね？ママ」　「そうよ。犬が西向きゃ尾は東っていうでしょう。」　「…じゃあ、もし南に向かったら？」

(“Sora ga kumottete mo, asa ha kuru yo ne? Mama.” “Sou yo. Inu ga nishi mukya o wa higashi tte iu deshou.” “…Jaa, moshi minami ni mukattara?”)

[“Mama, morning will come even if the sky is cloudy, right?” “That’s right. Just like if a dog faces west, its tail points east.” “…What if it faces south?”]

…Except this dog. [Source]