"Constant rubbing" refers to the act of repeatedly applying pressure or friction on something or someone for a prolonged period of time, which can have various consequences such as irritation or damage. Full definition
A few clinical signs of portosystemic shunt include abnormal behavior after eating, pacing and aimless wandering, head pressed against the wall or constant rubbing of his head (the blood not being filtered causes ammonia buildup, which makes his head feel funny), and constant illnesses (since the liver is not filtering the blood, it causes toxicity in the blood, making your dog constantly ill). (animalbehaviorcollege.com)
Other signs of plant allergies are watery irritable eyes, rash on the belly or other hairless areas like the nose constant rubbing and itching and biting their feet which are usually related to a grass allergy. (petseed.com)
general alopecia (hair loss), caused by constant rubbing against the metal bars in their small cages (yourpurebredpuppy.com)