Mishnah Niddah 6:9: Any [fish] that has scales has fins. But there may be one which has fins but does not have scales. Any [animal] that has horns has [split] hooves. But there maybe be one which has [split] hooves but does not have horns.

כֹּל שֶׁיֶּשׁ לוֹ קַשְׂקֶשֶׂת, יֶשׁ לוֹ סְנַפִּיר. וְיֵשׁ שֶׁיֶּשׁ לוֹ סְנַפִּיר וְאֵין לוֹ קַשְׂקֵשֶׂת. כֹּל שֶׁיֶּשׁ לוֹ קַרְנַיִם, יֶשׁ לוֹ טְלָפַיִם. וְיֵשׁ שֶׁיֶּשׁ לוֹ טְלָפַיִם וְאֵין לוֹ קַרְנָיִם:

Mishnah Niddah 6:10: Any [action] that requires a blessing after it requires a blessing before it. But there may be one that requires a blessing before it but does not require a blessing after it.

כֹּל הַטָּעוּן בְּרָכָה לְאַחֲרָיו, טָעוּן בְּרָכָה לְפָנָיו. וְיֵשׁ טָעוּן בְּרָכָה לְפָנָיו וְאֵין טָעוּן בְּרָכָה לְאַחֲרָיו: