Felines need thiamine (aka vitamin B1), and tests of the product show an insufficient level, putting those dining cats at risk for a thiamine deficiency if this is their only food. In early stages, this illness consists of excessive salivation, loss of appetite, and vomiting. As it worsens, symptoms include wobbly gate, seizures, and a downward curving of the neck (called ventroflexion). While risky, if caught promptly, it can easily be reversed.
For kitties that come running at the sound of an Iams ProActive can opening, be warned: Proctor and Gamble issued a voluntary recall of this food for both cats and kittens. If you see a can dated from 9/2011 to 06/2012, discard it and contact P&G for a refund.