
Marthian |

Cackle (Su): A witch can cackle madly as a move action. Any creature that is within 30 feet that is under the effects of an agony hex, charm hex, evil eye hex, fortune hex, or misfortune hex caused by the witch has the duration of that hex extended by 1 round.
Slumber isn't affected by Cackle. As for whether she could do it, probably no (unless she has water-breathing or something.)

Richard Leonhart |

she should be able, but it should also work if she cackles above water and the crocodile is less than 30 feet away.
It is not a sound based affect I believe.
Your GM is free to rule otherwise though as the fluff strongly suggests that you make a sound.
Edit: I completly forgot to think about slumber, yeah of course as Marthian said this doesn't work. For the rest, I'm not so sure, she would start drowning faster, but any human can make a sound underwater, even if you can't understand the words.

StreamOfTheSky |

The target is not required to hear you cackling in order for the cackle to extend the duration. Otherwise the Scar benefit would be pretty pointless and keeping the Charm hex going would be impossible in any social situation.
As for if she can underwater...I don't know. You can make a muffled sound of laughter with your mouth closed, so I'd probably just allow it. If she had Water Lung hex active or any other ability to breathe water, she absolutely should be able to.

harmor |

I asked this question to James to see what he says. Perhaps a FAQ can be added to clear this up.

blue_the_wolf |

as noted cackle does not effect slumber.
cackle seems to be an action important to the witch only. not the target.
what i mean is as long as the witch makes a cackle action it doesn't matter if any one is deaf, blind, under silence, tied up, or in any other way hindered. I have even allowed a witch to cackle while stealthed by giggling under her breath.