Okay, this is gonna be a strange question.
The character just says out of the blue (in order to lighten the mood) :
ハナクソの秘密をそっと話{はな}くそう!! [with dots above the seconds は、な、く and そ]
Is it just a pun on 話そう？ => Let's talk discretely about the secret of the snot!!
Like, I don't know, if there was a verb "to sno" in english meaning "to speak" and the speaker voluntarily pronounced it "snoT" instead of "sno" : Let's snoT discretely about the secret of the snot!!
