What are 'compulsive habits'? What does Maxwell say are the compulsive habits of(i)school children (ii)Mij?

'Compulsive habits' are strange acts of behaviour which one does without a particular reason.

School children on their way to school and back placed their feet on the center of the each paving block. Similarly, Mijbil would tug the author to the two feet high wall of a school when he walked with him. On his way home, he made it a habit of jumping on to the wall and go galloping all along its length of thirty yards.