Mineral oil is used by mant pet owners as a treatment for hairballs in cats and constipation in both dogs and cats. However, when given by mouth, mineral oil is easily inhaled, especially if a pet struggles while receiving it. If this happens, lipoid pneumonia (lung inflammation caused by inhalation of an oily substance) can result. And that's not good.
Usually when people or animals aspirate something in to the lungs and airways, the cough reflex kicks in immediately to rid our lungs and airways of the substance. But this isn't always the case when an oil like mineral oil is accidentally inhaled. This is because the oil can actually coat the airways and calm the cough reflex. As a result, it is not coughed up and stays within the respiratory tree, causing a foreign body inflammation and leaving the lungs suceptible to bacterial infection. As the inflammation increases, coughing will increase, but by that time, its too late..the stuff is there to stay.
If your pet is suffering from constipation or in the case of cats, hairballs, there are a number of much safer and more effective products to use as remedies. Talk to your vet about which one would be right for your pet's particular condition. But remember: Mineral oil is not one of them.