Pesachim 81: Do You Know Where the Bodies Are Buried?

More on Tumat ha-Tehom. First, the Gemara establishes a kal va-chomer (a fortiori) regarding the unknown impurity as derived from known purity. And then the Gemara knocks down that logic as illegitimate reasoning in this case. Rather, the particulars of Tumat ha-Tehom emerge from a whole slew of biblical verses, right? In fact, not quite, as the Gemara recasts those verses as "asmachta be-alma," a way to connect the halakhah to the text, but really the case of Tumat ha-Tehom is "halakhah le-Moshe mi-Sinai." Also, how all this comes to pass in practice - for example, how one might inadvertently, unknowingly come in contact with a dead body. And that body must be complete, in contrast to the usual tiny measure for Tumat Meit.