Q: My five-month-old Miniature Dachshund loves to lick the walls of my home. He will wake up in the middle of the night, go to the toilet, and lick the cement walls there. Some days, he’ll lick the walls of my living room. Is this normal or is it a sign that he’s suffering or sick?

This is one of those quirky behaviours that both healthy and unwell pets may do. We had a cat that used to love to lick condensation from inside windows on a cold morning in the U.K.. He was very well and it seemed to be something he enjoyed doing. There are many unsupported theories from vets and lay people as to why, and yet no solid research has been done.

One of the most often given reasons for dogs licking—people’s legs especially—is that they like the saltiness. Animals, like people, do seem to like the taste of salt. Cattle and horses were once provided salt licks, until it was found some individuals had a lot and some were never interested in them. From all of this, it seems logical to presume that we have all probably evolved to like salt in small amounts, as it’s essential for health. However, salt is poisonous in large doses.

Some vets and pet owners believe that animals know which essential minerals they are lacking, which is why they eat (or lick) certain substances containing the missing mineral. But that’s a myth. Potassium-deficient cats do not go looking for green leafy vegetables. It’s just salt that both humans and animals have an appetite for.

There are conditions that cause pica (an appetite for substances that generally have no nutritional value) or depraved appetite, but it’s largely restricted to brain disease and phosphorous deficiency in cattle. In cases where there’s a medical condition, the pica is not just a passing fancy—it’s usually extreme and the animal will ingest non-food items regularly. In phosphorous-deficient cattle, they eat all sorts of things they would not normally, like bark and leaves. The suggestion that a range of diseases is responsible for a depraved appetite in pets is, in my view, probably an exaggeration. Some diseases do increase appetite, but it’s for normal food.

The salt that forms on the surface of concrete (efflorescence) is often a combination of calcium sulphate (gypsum), salt (sodium chloride) and calcium carbonate (calcite). It’s logical to assume that these appear in small quantities on the surface of all concrete. It seems that all animals like the taste of salt to a greater or lesser degree, and it seems more palatable when it’s in small quantities.