Believe me-- it's more normal than you think it is. We have dogs that like to sniff around the cat litter boxes and take 'treats' from it-- we have no idea why they find it so appetizing.
A lot of animals have this behavior-- and it's pretty disgusting, I agree, but it is normal.
If you're curious, try reading this article:
http://www.cvm.uiuc.edu/petcolumns/s...cle.cfm?id=166