When I was little, I was told that milk got spoilt during this period due to the mysterious radiation from Sirius, the Dog Star. Also, the bodies of people who had drowned at sea would float up to the surface.
From Wikipedia: Dog days - Wikipedia, the free encyclopediaThe dog days are the hottest, most uncomfortable part of the Northern summer.[a][1] The American weather and farming annual, The Old Farmer's Almanac, explains that "[t]he phrase 'Dog Days' conjures up the hottest, most sultry days of summer," coinciding with the heliacal rising of Sirius, the dog star, in the constellation Canis Major.[2][3]:19 While the correlation between the hottest and most humid weather of the year with this specific calendar period has not survived the broadening of weather understanding and communications to global, the correlation of the rising of Sirius with extreme heat has been sufficient in enough climes in the Northern Hemisphere such that the association of dog days "with hot, sultry weather was made for all time."[2]