[it's surprising that venti doesn't know... but do people like him think about such things? does mondstadt not have doctors, only magical healers? kaeya's comments seem to make him think so.]

Mm. It works that way. [then he takes venti's hand to place the bottle in it.] Just dab a little bit onto the wound, or even a ball of cotton and gently wipe it. No need to upend the whole bottle onto the cut, so you can save it for later. All right?