This was a very famous advert at the time. One of the iconic adverts of the 1980's really.
It featured an animated dragon, voiced by Willie Rushton. He was a Dragon, you see, with terrible breath (as you would imagine a fire breathing dragon would have...) but Listerine meant that he could win the girl with his minty fresh breath.
The advert always confused me as it seemed to show the dragon "Clifford" seemingly swallowing the listerine - something that my mother strongly told us NEVER to do (by her tone I thought we might die!) On reflection maybe Clifford was vaporizing the Listerine into steam so it just disappeared.
Still, to my small mind it was confusing.
Listerine fact - before they decided to make it a teeth cleaning product, the makers of Listerine tried to market it as floor cleaner! And anyone who's tried it can testify that it has a KICK to it!