after the infirmary

Marius is attempting to resist the overwhelming impulse to cling to Cosette's skirts like a little boy in this strange place. But he's not a little boy, Cosette has her father to think of-- and apparently, they are not the only people here that he knows.

So Marius is exploring. Though he hasn't gotten very far, because he makes his way down each corridor very slowly, as if afraid the ground will give way beneath his feet at any moment; rounds each corner with as much caution as if he expects some monstrosity to appear at every turn.