Scroll allll the way to the bottom of the creatures file and you'll see some example blocks. Here's some of the stuff you'll want. You'll have to change the parameters though:
300;//interval in milliseconds - The interval in which it repeats, 300 is a nice number
15;//condition number - The distance the player has to be before they start their stuff
47;//effect number -say stuff
???.000000;//parameter1 - the dialog in which to say (see dialog file)
22;//effect number -Change side effect number
???.000000;//parameter1 -which side do you want? The human is side 0 by default.
-1.000000;//parameter2 -how long should it be this side for? (-1 is forever)
???.000000;//parameter3 -any special effects wanted from weapons? Set to -1 for none.
Avoid doubling up on "begin" and "end" lines. It happens!