Example of mild OCD ritual
Samuel Johnson famous 18th century writer had this compulsive ritual as described by his friend James Boswell.
He (Samuel Johnson) had another particularly, of which none of his friends ever ventured to ask an explanation. It appeared to me some superstitious habit, which he had contracted early, and from which he had never called upon his reason to disentangle him. This was his anxious care to go out to go out or in a door or passage by a certain number of steps from a certain point, or at least so that either his right or his left foot, (I am not certain which) should constantly make the first actual movement when he came close to the door or passage. Thus I conjecture: for I have upon innumerable occasions, observed him suddenly stop, and then seem to count his steps with a deep earnestness; and when he neglected or gone wrong in this sort or magical movement, I have seen him go back again, put himself in a proper posture to begin the ceremony, and, having gone through it, break his abstraction, walk briskly on, and join his companion.... it is requisite to mention, that while talking or even musing as he sat in his chair, he commonly held his head to one side towards his right shoulder, and shook it in a tremendous manner, moving his body backwards and forwards, and rubbing his left knee in the same direction, with the palm of his hand. In the intervals of articulating he made various sounds with his mouth, sometimes as if ruminating, or what is called chewing the cud, sometimes giving a half whistle, sometimes making his tongue play backwards from the roof of his mouth, as if clucking like a hen, and sometimes protruding it against his upper gums in front as if pronouncing quickly under his breath too, too, too: all this accopmpanied sometimes with a thoughtful look, but more frequently with a smile.