You see: You gasp! Others see: <Person> gasps!
GASP <self> You see: You hold your breath. Others see: <Person> holds <his/her> breath.
GASP <person> You see: You gasp at <Person>! Target sees: <Person> gasps at you! Others see: <Person1> gasps at <Person2>!
GASP (while hiding) You see: You gasp, though no one can see you doing it. Others see: You hear someone gasp!