– but an unfelt sting
(Shika no tsuno wo hachi ga sasu; “A wasp stings a deer’s antler”)
In literal terms, this phrase refers to something that doesn’t even tickle or itch, much less hurt; something that elicits no response or feedback. Like a bee or wasp stinging a deer’s (fully developed) antler, which is (presumably) largely unable to register pain. In actual usage, the pain in question seems to be the mental pain that comes from one’s own failures, and the unfeeling response indicates that the person in question is remaining blithely, or even willfully, oblivious instead of facing, repenting of, and working to repair their flaws or failings.
We begin three characters in with the noun 角 (tsuno), “horn,” attached (and shown as belonging) to the noun 鹿 (shika), “deer,” by the associative particle の (no). This noun phrase as a whole is marked by the particle を (wo) as the direct object of a verb. The subject of the verb, marked by the particle が (ga) is the noun 蜂 (hachi), “wasp” or “bee,” and the verb in question is 刺す (sasu), “to stab,” “to sting,” in conclusive form.
An older reading renders 鹿 as shishi, but that seems to be the less common form now.
Apparently this comes from a 1715 joururi play titled 『心中恋の中道』 = Shinjuu koi no nakamichi.
(“Kaito-san wa sensei no hochikisu wo karite nakushita kara sugoku shikarareteta kuse ni, kyou wa sero teepu wo kashite kashite tte itte, shika no tsuno wo hachi ga sasu da. Shinjirarenai.”)
[“Even though Kaito got seriously chewed out for borrowing and then losing the teacher’s stapler, today it was all ‘lend me your tape, lend me your tape,’ absolutely impervious to learning anything. Unbelievable.”]