While playing through a Paizo Adventure Path my players came across an encounter that began with a group of tengu firing poisoned darts at the party from blowguns. One of my players had the grace to ask about that fact. Since tengu have crow like beaks in place of mouths, wrapping one's lips around the mouth of a blowgun becomes rather difficult when one does not have lips.
I, of course, told him to be quiet and get me a beer. However, it left me thinking what the designer must have had in mind. Giving them the benefit of the doubt and assuming they did not forget about what a tengu looks like.
I really want to know if there are any additional resources that address the seeming contradiction of this weapon use, or you've managed to make up a story good enough to convince your players.