TT #163 · Parshas Shemini · Aliyah 6 · Passuk 29
Chabad.org — Vayikra Chapter 11 with Rashi
English: These are the creatures that are impure among the swarming things that swarm on the earth: the weasel, the mouse, and the various kinds of lizard.
Nazir 64a.
E-Daf.com — Nazir 64a (Tsurras Hadaf)
בַּשֶּׁרֶץ הַשֹּׁרֵץ עַל הָאָרֶץ. כְּתִיב בַּשֶּׁרֶץ הַשֹּׁרֵץ כָּל מָקוֹם שֶׁהוּא שׁוֹרֵץ, וּכְתִיב עַל הָאָרֶץ, הָא כֵּיצַד? וַדַּאי מַגָּעוֹ טָמֵא, סָפֵק מַגָּעוֹ טָהוֹר, מִכָּאן לְסָפֵק טֻמְאָה צָפָה בֵּין בַּכֵּלִים בֵּין בַּקַּרְקַע טְהוֹרָה.
Certainty distinction — The doubled wording distinguishes definite contact, which conveys impurity, from doubtful contact, which does not.
Certain contact with floating impurity is treated differently from uncertain contact, yielding the rule of floating doubtful impurity.