Courfeyrac likes to play the bagpipes at times of stress, in an attempt to calm the group or add solemnity to important and monumental occasions. To spare his feelings, his friends simply endure the racket, their smiles etched fixedly upon their faces and Enjolras' foot tapping impatiently, like the ticking of a bomb about to explode.
On the night Marius announces his engagement, they almost believe that the noise will never stop, and Cosette's smile falters (although she insists that the tears in her eyes are born of happiness and excitement).
In an attempt to salvage the situation, Grantaire and Feuilly mime a dramatic and solemn dance, which makes them laugh but unfortunately does nothing to cure Joly's headache.
Upstairs, where Eponine has chased down Enjolras once again to seek comfort in his arms, the pair instead lay side by side in indignation as the bagpipes erupt through their eardrums like nails dragged across a blackboard. If truth be told, Enjolras thinks to himself, he is half dreading the day the rebellion kicks off, for the chosen date is drawing near and the prospect of such a fanfare may bring the enemy straight to their doorstep.
Turns out you needn't have worried, Eponine laughs at his scowling face weeks later.
(As the wailing screeches ring across the rooftops of La Rue de la Chanvrerie, the National Guard are deterred for yet another night).