Commentary Inf VI 91-93
Ciacco's last 'gesture,' his glance moving from Dante's face and going vacant, has been a puzzle to many readers. The commentary of Bosco/Reggio is clear and to the point: 'Ciacco passes from his temporarily fully-human phase to one of nearly pure animality; first he looks askance; then he continues to fix Dante with a stunned gaze in which, bit by bit, any last trace of humanity is extinguished; then his head droops, deprived of any human vitality; finally he falls headfirst into the muck, unfeeling and inert' (DDP Bosco.Inf.VI.91-93).

For Ciacco's being in a state of 'hebetude,' the condition that theologians connect with gluttony, see DDP Singleton.Inf.VI.91-93.

Padoan's gloss (DDP Padoan.Inf.VI.92) suggests that for Ciacco this experience is akin to that of a second death. Indeed, we see him arise from death, called back to his vital former self when he hears his native speech; now he 'dies' all over again.