matching columns and producing results

I have 2 columns of data looks like this:

col-a
shark
whale
dolphin
seal
fish

col-b
dog
cat
fish
deer
moose



What I'm looking for is a formula to compare col-a to col-b and create col-c to look like

col-c
dog
cat
deer
moose

Cross post here

http://www.ozgrid.com/forum/showthread.php?t=77529

Thanks,
Chris