Knowing the pet food labeling "rules" helps rather than just blindly buying all one or the other.

http://www.fda.gov/cvm/petlabel.htm

My favorite myth is people being sensitive to the formalgahyde in certain beers (my husband won't drink Budweiser because it gives him a headache and he claims it's from the formalgahyde). Formaldehyde is a poisonous gas and is not used in the making of any commercial beers, US or foreign.