<<...I always wondered why chickens were considered clean due to the fact that they are scavengers. Anyone know why?

Elaine, 

Nice to see you over here :-)... don't have an answer to your question but was similarly wondering about all those 'flat fish' like sole... they're considered 'clean' by followers of biblical diets [have scales and gills] yet all are 'bottom feeders [scavengers]... 

Dedy