The Shulhan Arukh records that the mention of the ten sons of Haman must be read in a single breath. This commemorates the fact that they were hung at the same time. Today in many Synagogues, the hazan first pauses to allow the congregation to read the ten sons of Haman in a single breath and then s/he repeats the ten sons in a single breath. Why not rely on the hazan to read them in a single breath, like we rely on the hazan to read the rest of the Megilah? The Rogatchover famously explained that the hazancan read on behalf of the congregation but he cannot breathe on behalf of the congregation.