I suppose you could install a small gas cylinder in the grip trap so as the cobra rears up it gives a hiss. Certainly a work of art and a conversation piece. Would obviously do the job in the field for anyone brave enough to take it.
I never really got to like the style of foresight on the Rigby's, mounted back from the muzzle with an abrupt front edge, almost as though it is waiting to be threaded for a suppressor. Now come to think of it, let the imagination run riot on what could be engraved on a suppressor.

Jokes aside, a rifle with nice lines for a good handy cartridge. Maybe an image of Jim Corbett would set off the Kumaon nicely?