The boys begin referring to their murder of Simon as "the dance" because they were doing their brutal, savage dance when he stumbled upon them and they "mistook" him for the beast. They do not directly refer to it as murder and Jack even tells his boys that they could never have murdered the beast, that he must have come in disguise. Arguably, the boys lie to themselves about this memory as a form of extreme denial, not able to face just yet what they are capable of. This stands in stark contrast to when Piggy is brutally and purposefully murdered - no one is in denial about this murder; they are more capable by the end of the novel of facing their inner savage, even of embracing it.
Jack orders that Wilfred be tied up and beaten. Wilfred himself in not an overly significant character, but is used in this instance to demonstrate Jack's method of leading, which includes torture for no reason whatsoever.