Some netizens praised the men for choosing to rest rather than drink and drive.
Only the body of the 17-year-old daughter was found while the other victims are still missing.
The rats had allegedly chewed through the wires of one woman's car, preventing it from starting.
A coffeeshop stallholder said that the group has been playing cards at the spot for at least four years.
She said she initially thought it was a sour plum.
This year marks the hottest July in Japan since records began.
Authorities found no signs of struggle.
The elderly man allegedly paid S$16.50 for a mixed rice dish that cost S$6.50.
The man was diagnosed with bone marrow suppression, a dangerous condition that affects production of blood cells.
"Chickens, rabbits, and guinea pigs make up an important part of the diet for our predators," the zoo wrote.