Shalom! What would Rav Chisda hold about a fat man's stomach (but not his bone) in a bathroom and saying shema at the same time? What about the belly of a pregnant woman (where the bone of the fetus is in the bathroom but none of the Woman's bones)?
Thank you! Chag Kasher Vsameach!
Gavriel Bensimon, Silver Spring, MD USA
1) It seems that Rav Chisda is not referring literally only to bones. Rather, Rav Chisda understands that "All my bones will say..." means that one's entire body should praise Hash-m, and therefore the entire body must be free of "Tzo'ah."
2) This may be seen in the words of the Rashi who explains that Rav Huna derives from the word "Neshamah" that only the mouth and nose are included in the praise of Hash-m, and not the other limbs. It seems that Rashi learns that since the word "Neshamah" is related to "Neshimah," which means breath, we derive from this that it depends on the limbs through which one breathes, i.e. the mouth and the nose, and since these are also the organs which are able to smell, we learn from here that only the latter limbs must be free of Tzo'ah.
3) Hence, Rav Huna is in fact quite a lenient opinion, because he is particular only about the mouth and the nose. Rav Chisda, in contrast, is more stringent and requires the entire body to be clean, even the parts which are not capable of smelling. This may be seen in the words of the Rosh (3:45) who writes that according to Rav Huna, if one cannot sense a bad smell, he is permitted to say Shema. However, according to Rav Chisda if the excrement is on one's flesh, or one's hand is inside the bathroom, one may not say Shema even though one cannot smell anything bad. The Rosh writes that Rav Chisda learns from "All my bones will say" that the entire body must be clean, even though one cannot smell anything bad. The words of the Rosh, that the entire body must be clean, suggest that it does not depend literally on the bones, but rather we learn from the verse that the entire body must be clean even if the person does not sense a bad smell.
4) The fact that Rav Chisda is more stringent than Rav Huna, not more lenient in certain cases as your question hints at, also seems apparent in the words of Talmidei Rabeinu Yonah in their commentary on the Rif. On the first line of 16b (in the pages of the Rif pages), Rabeinu Yonah cites Rav Hai Gaon and other commentators who ruled according to the stringent opinion of Rav Chisda. This suggests that Rav Chisda is more stringent. I did not find any of the commentators who write that one could also find a leniency according to Rav Chisda -- that if a person had no bones inside the bathroom, he could say Shema even though a bad smell reached him. This seems to be prohibited according to all opinions.
Kol Tuv,
Dovid Bloom