TIME July , midsummer
In EDO period, there was HARUKIYA ZENBEI at eel shop in Kanda.On summer day, TOUDOU who was a daimyo, placed an order with him for a lot of broiled eels. So, he kept on broiling eels for three days(the Rat,the Ox and the Tiger), and he put them into earthenware pot on each day.
On the appointment day, he took out the broiled eel from the pot. Then, the eel broiled on the Rat and the Tiger day discolored and tasted bad, but the eel broiled on the Ox day didn't change.
So, it is said that the Ox day is suitable for broiling eels.