Wards are small benign lumps of the skin.
Warts may develop anywhere on the body and have diverse shapes. Normally, they are not larger than a pea and feel soft. The contact to the skin is only thin and consequently the ulcer is well movable. The surface is rose to rosy and appears wrinkled or reminds slightly of a small cauliflower.
There are certain types of viruses which result in the growth of warts. Most warts are rather to be considered as symptom of old age.
Provided the nipple is not injured or angry or causes any disorders, it is left as it is.
A wart should not be removed on its own, neither when it seems to be very flexible. It may result in injuries and inflammations of the skin. Basically, it is the best to observe the respective area. If the wart becomes larger, then as soon as possible a veterinarian should be consulted.