Mishnah Tevul Yom 1:3: A nail-shaped knob on the back of a loaf [that serves as a sign], or a small grain of salt [stuck to a loaf], or a burnt crust less than a finger's breadth [are all rendered impure impure by contact with a tevul yom and render the loaf impure as well]. Rabbi Yose says: whatever is eaten along with it [i.e. with the loaf] is rendered impure [and renders the entire loaf impure upon contact] with a tevul yom; and it is needless to say [that this is the case] regarding all other impurities.

מַסְמֵר שֶׁאַחַר הַכִּכָּר, וְגַרְגֵּר מֶלַח קָטָן, וְחַרְחוּר פָּחוּת מִכָּאֶצְבַּע, רַבִּי יוֹסֵי אוֹמֵר, כָּל שֶׁהוּא נֶאֱכָל עָלָיו, טְמֵאִים בִּטְבוּל יוֹם, וְאֵין צָרִיךְ לוֹמַר בְּכָל הַטֻּמְאוֹת:

Mishnah Tevul Yom 1:4: A pebble in a loaf, or a large grain of salt, or a lupine [in a loaf], or a burnt crust more than a finger's breadth [are not rendered impure]. Rabbi Yose says: whatever is not eaten along with it is pure [even after coming into contact] with an Origin of impurity; and it is needless to say [that this is the case] regarding a tevul yom.

הַצְּרוֹר שֶׁבַּכִּכָּר, וְגַרְגֵּר מֶלַח גָּדוֹל, וְהַתֻּרְמוֹס, וְהַחַרְחוּר יָתֵר מִכָּאֶצְבַּע, רַבִּי יוֹסֵי אוֹמֵר, כֹּל שֶׁאֵינוֹ נֶאֱכָל עִמּוֹ, טְהוֹרִים בְּאַב הַטֻּמְאָה, וְאֵין צָרִיךְ לוֹמַר בִּטְבוּל יוֹם: