Laudator Temporis Acti

Cicero, On the Laws 2.15.39 (tr. Niall Rudd):

I do notice how in theatres which once used to be filled with the agreeable plainness of Livius' and Naevius' tunes audiences now rock to and fro jerking their necks and eyes in time with the inflexions of the singer's voice. Ancient Greece used to punish that sort of thing severely. It foresaw far in advance that the deadly plague, gradually creeping into the citizens' minds and infecting them with pernicious crazes and pernicious ideas, would suddenly bring about the collapse of entire states...

The Latin text with an image of the critical apparatus from J.G.F. Powell, ed., M. Tullius Ciceronis De Re Publica, De Legibus, Cato Maior De Senectute, Laelius De Amicitia (Oxford: Oxford University Press, 2006), p. 217:

Illud quidem <video>: quae solebant quondam compleri severitate iucunda Livianis et Naevianis modis, nunc ut eadem exsultent, <et> cervices oculosque pariter cum modorum flexionibus torqueant. Graviter olim ista vindicabat vetus illa Graecia, longe providens quam sensim pernicies illapsa civium <in> animos malis studiis malisque doctrinis repente totas civitates everteret...

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Thanks to Eric Thomson for drawing my attention to another conjecture, by Harry Morgan, Music, Spectacle, and Society in Ancient Rome, 168 BC – AD 68 (Ph.D. thesis, Oxford, 2018), p. 80:

... nunc ut eadem exultent <theatra, et tibicines> cervices oculosque pariter cum modorum flexionibus torqueant ...