Yevamos 34

R' Meir says that one can also transgress the Issur of carrying on Shabbos (while eating all those Issurim) by walking out on Shabbos and swallow it in a Reshus Harabim. Tosfos asks why should he be Chayiv? The Gemara exempt people who carry out objects in their mouths, since it's a Shinoi (since most people carry thing in their hands. Tosfos answers: though most objects are that way, however, food is different, since it's the regular way to carry food in your mouth when you're eating. Rabbi Chaim Smulowitz If you ever though that Tosfos was beyond you. Think again. A few more free copies of Gemara and Tosfos: Sukka 2a-11a is still available at https://www.tosfos.ecwid.com