M. Alice: Ever since I began to choose the plastic bags over the paper ones to bring my groceries home, I've observed a very strange behavior in my cat. She seems obsessed with licking the plastic bags! A friend’s cat seems to be hooked on them too. What’s in the plastic that’s driving our cats crazy or are they just crazy? — Kristi, New Orleans

In the course of tracking down an explanation, I encountered several others who’d notice same behavior and one person with a dog that ate all her Tupperware lids. Perhaps it’s just the animal kingdom adapting to our all-petroleum-byproduct world.

But I think we’ve found a logical answer to this poser. Or at least semi-logical, giver the question has to do with cat behavior. Lightweight plastic film products are manufactured with something called a slip agent, which makes the film easier to handle. The slip agent is added to the resin and “blooms” to the surface of the extruded film. The base for the slip; is often a processed form of vegetable oil or animal fat. So the best guess is that the cats are licking bags made with an animal-fat-based slip agent.

The FDA mandates the types of slip agents that can be used on plastics destined for grocery bags, and none of these can be toxic. Most people I talked to guessed that no harm come to the cats from licking the bags, but you might check with a vet to be on the safe side.