The dog days are over
The dog days are done
The horses are coming
So you better run
A ‘dog day’ is an astronomical reference to a day that lies between July and August, when the Sirius constellation can be seen. This constellation is also known as the Dog Star. In Roman folklore, the appearance of the Dog Star was said to bring the hottest day of the year. Hence, Florence’s “Dog Days (Are Over)” deals with the end of a Golden era, and moving forward regardless of who you have to leave behind to do that.
The chorus of the song also contains a biblical reference. “The horses are coming” is a line from the Book of Revelations, in which horses are described as the carriers of destruction:
“The black horse that will bring famine and inflation; the red horse which will bring war and [...] behind the pale horse hell will follow.”