A boy can have zero displacement while covering a non-zero distance in two cases. First, if he walks in a straight line and then returns to the starting point, his displacement will be zero because he ends up where he started, even though the distance covered is the total length of the path he walked. Second, if he moves in a circular path and completes one full circle, his displacement is zero because the starting and ending points coincide, but the distance covered is the total length of the circular path, which is greater than zero.