Hi,
Well I generally say things like "aww isn't that adorable!" or on occasion "let go ya wee bugger!"
Best advice is to try and remain calm and not to pull away or make any sudden movements.
I sometimes have good luck with distracting them by keeping them moving or pointing their heads towards a tv screen ( yes I know it sounds nuts) - I figure that if they don't get a chance to "lock onto" something they are less likely to strike. And of course if there is something in front of them changing they are too busy watching it and assessing it for threat to think about striking at the thing they are sitting on.
And once they have been sitting in your hands for a good length of time without getting hurt they tend to relax a little and come out of the strike pose all on their own.
Not all of that works all the time though.
dr del