As we learned yesterday, according to the first Mishna in this perek, mixtures that contain hametz are prohibited only on the level of a simple negative commandment, which does not carry the same punishment – karet as pure hametz if it is eaten. Rav Nahman identifies the author of this opinion as Rabbi Eliezer, quoting a baraita in which Rabbi Eliezer teaches that eating pure grain hametz is punishable by karet, while eating hametz in a mixture is a lav – a simple negative commandment, punishable by lashes. The baraita includes the opinion of the hakhamim, who agree that eating normal hametz will be punished by karet. With regard to eating a mixture containing hametz, the hakhamim rule that it is b’lo klum – “there is nothing.” At first glance it would appear that the hakhamim feel that such a mixture is permitted on Pesah.
Nevertheless, the Rif and the Rosh (and, based on their ruling, most of the codifiers of halakha) rule that the expression b’lo klum in this case does not mean that it is permitted, rather that there is no punishment for eating it since the requisite amount needed to be held liable would not be eaten. After all, even if someone ate a full ka-zayit (olive-size amount) of this mixture, he still will have eaten less than a ka-zayit of hametz. If we understand the opinion of the hakhamim this way, were a person to eat a very large portion of the mixture that includes hametz, so that tokh k’dei akhilat pras – within the amount of time that it takes to eat half a loaf – he ate a full ka-zayit within the mixture, even they would agree that he would receive the punishment of lashes.
The Gemara concludes that Rabbi Eliezer also will forbid hametz nuksheh (hardened leaven) on the level of a lav. The Ritva explains the term hametz nuksheh as referring to hametz that is not edible or has not been fully baked, that is to say that it is not the full hametz referred to by the Torah.