Nighttime mouth strikes again!

An excellent, unintentional counter. Of course, the unintentional recoil is a bitch, but, still...

I think they bumped teeth, actually.

Satori bumped teeth while Koishi got her mouth, not really bitten, but caught in the middle?

Looks to me like Satori bit Koishi's tongue to counter her impending lick, not realizing it'd be...well, putting her sister's tongue in her mouth.

Desperate times call for desperate actions