The settings that you will need to use really depends on the effect that you are going for.
If you want some motion blur in the photo to show motion of the croc then use a slower shutter speed 1/10-1/50 of a second will do depending on how much blur you want.
If you want the blur with a core sharpeness to the image then set it into manual mode and choose the shutter speed to taste and then use the flash in rear sync flash mode to freeze the motion.
If you want to freeze the motion completely then you will need to use a fast shutter speed. Something like 1/200 or faster depending on how fast the subject is moving. And crocs move pretty fast when eating.
__________________
Rex K
The view from my "office" doesn't suck. 
|