Tohoros 5:1-2

Tohoros 5:1

Let’s say that there’s a dead vermin (which imparts impurity) and a dead frog (which doesn’t) in the public domain – and the same is true of an olive-sized piece of a corpse and an olive-sized piece of carrion (neveila), a bone from a corpse and a bone from neveila, soil from Israel and soil from a plowed grave (beis ha’pras), soil from Israel and soil from elsewhere – or if there were two paths, one ritualy unclean and one ritually clean, and a person walked on one of them but we don’t know which – if a person overshadowed one of each pair but we don’t know which, or if he moved one of them but we don’t know which, Rabbi Akiva rules the person unclean and the Sages rule him clean.

Tohoros 5:2

If a person says that he touched something but he doesn’t know whether it was unclean or clean, or that he touched one of the two things but he doesn’t know which one, Rabbi Akiva rules him unclean and the Sages rule him clean. Rabbi Yosi says that one is unclean in all of these cases; one is only clean in the case of the path because people usually walk but they don’t usually go around touching things.