Too much of nearly anything can be harmful, so try to vary your treats. Some popular suggestions: a slice of banana (mashed, so it’s more digestible), raisins, peanut butter, bits of pear, peppermint (small licks), freeze-dried liver (sold as cat treats), Pounce cat treats, puffed rice cakes, green beans, wheat crackers, Ferretone, Petromalt. Try feeding your ferret pretty much anything, in small pieces.
You never know what yours will consider a fabulous treat. I’ve heard of ferrets going wild for everything from spaghetti to blueberries. Although most ferrets love milk and ice cream, they shouldn’t be allowed to have much. This is especially true for young kits, since the lactose in cow’s milk gives ferrets diarrhea, which can easily cause them to become dehydrated. Goat’s milk, available in some pet stores, is okay. Likewise, I’ve heard that soy milk is good for them and generally liked, but I haven’t seen any verification. Too much fiber can also give ferrets diarrhea, so limit raisins, bananas, prunes, oatmeal, apples, and anything with bran in it. Sugary treats aren’t good for them either, since they can cause dental problems. (Despite the rumors, there is no evidence that sugar causes diabetes or other metabolic problems in mammals.)
Be careful with chocolate. Most ferrets like it, but the xanthines/theobromine found in it may be toxic to them in large enough quantities; nobody’s sure. It’s not recommended as a treat. (However, many people give their ferrets an occasional chocolate chip with no problems.) Likewise licorice – the real thing, not the plastic, fruity, red stuff that goes by the same name – is surprisingly strong. It’s been used for medicinal purposes in the past; it might not be a good treat. Both chocolate and licorice are more likely to be dangerous to ferrets with heart problems . Onions, garlic, and other members of that family can cause Heinz body anemia in dogs and cats; nobody’s sure about ferrets, or what the dangerous dose might be (the tiny bit in some meat baby foods is probably fine), but caution is advised.