Parashas Metzora · Passuk 15:11
Chabad.org — English translation + Rashi
Torah Temima points to Kiddushin 25a (verified on the daf).
E-Daf.com — Tsurras Hadaf (size=3)
HebrewBooks / Shas PDF of the daf
English: “And whoever he touches” — Ulla said: All agree regarding the tongue for impurity that it is treated as exposed with respect to a sheretz; what is the reason? Scripture said “that he touches,” and this too is capable of contact.
Tongue as exposed for contact
Chazal treat the tongue as an exposed organ for contact impurity in this context.