According to one folk etymology, the rice ladle symbolizes housewives; since cats and housewives are virtually universal to Japanese households, the expression means “everybody.” An opposite interpretation holds cats to be rare and rice ladles to be universal, so that the expression is all-inclusive of both rare and abundant items.
A: Saikin mata sukaato take ga sukoshi mijikaku natta yoo ne.
B: Soo na no yo. Korede mata, neko mo shakushi mo mijikai sukaato ni naru n desho. Kosei ga nakute iya ni naru wa ne, mattaku.
B: そうなのよ。これで又、猫も杓子も短いスカートになるん ないでしょ。
A: It seems skirt lengths have shortened recently.
B: You noticed, too? Now everybody and her mother will be wearing shorter skirts. There’s absolutely no individual style- I hate it!