1 No flying creatures or creatures that run on four legs can be used.
Once the container is closed, the owner of the premises and his family must pray once every night before falling asleep, and once a day before waking up. This must continue for an entire year without interruption. During this time it is essential that no one outside the household is made aware that a Gu is being created on the premises, otherwise they will be visited by a sorcerer (巫师 wū shī), the Gu will be stolen (using a special kind of black magic), and the previous owner will die, alongside their entire family. In the event a sorcerer does not darken their doorstep, the Gu itself will harm its master when it's ready.
After one year when the container is opened, only one creature will be left. The Gu will have changed in appearance from its original form, in both shape and colour, of which there are a few common forms; 1. a Dragon Gu (龙蛊 lóng gǔ) which resembles a dragon - usually formed from a Gu snake, 2. a Qi Lin Gu (麒麟蛊 qí lín gǔ) which resembles a Qi Lin (麒麟 qí lín) - usually formed from a Gu frog or lizard, or 3. if following the practice where the final Gu's body is fed to larvae, a leech-like creature.
The Gu will then be kept in the container and placed in another secret location, dark and air tight. It is said that Gu's like to eat rice, especially egg fried rice cooked in pig fat. Over the next three to four years the Gu will grow to a size of one zhang (丈 zhàng)2 until they are finally ready to be released.
2 The length of one zhang (丈) has changed over time and is believed to have varied between 169.5cm and 316.8cm throughout the various dynasties, averaging around the ~263.3cm mark.
The Gu's master will chose an auspicious day to open the container and let the Gu fly out by itself. After a Gu leaves the premises, it will either transform into a ball of fire, will travel to and linger in the woods on the mountains, or become a shadow, moving silently and undetected between the houses in the village. When the Gu returns home, it will be placed back in it's original container. It's master will not need to feed it if it has killed that day.
A Gu's magic is most powerful at dusk, and though a single touch would be fatal to anyone or anything that comes into contact with it, the biggest advantage of raising a Gu is not to kill, it is to feed off of its aura (灵气 líng qì). With a Gu by his side, should a master want to do business, the Gu's aura will ensure he is profitable in his endeavours. However, the need for self control will be great, for if someone were to realise his good fortune were due to the presence of a Gu, it wouldn't be long until a sorceror arrived at their doorstep to steal the Gu away. Should this occur, the master and his entire family would die.
In addition to daily religious service, Gu masters must make a sacrifice to their Gu on the 24th day of the sixth month of the Lunar Calendar every year. This ceremony lasts for three days, namely the 24th, the 25th, and the 26th and during these three days, the master will prepare one fresh pig, one fresh chicken, and one fresh lamb every day, to be served to the Gu at night time.
Raising a Gu is an extremely difficult and dangerous thing to do, however, their are huge benefits to those practioners who are able to successfully cultivate a Gu and keep its existance a secret from the rest of the world. They are said to be used in black magic practices such as manipulating sexual partners, creating diseases, and causing death.
Gu's are loyal to their masters. In one version of the legend, in a tribe that lives on Xue Ling Mountains (雪岭山 xuě lǐng shān), all girls must raise a Gu of their own when they reach the age of 12. This Gu becomes their guardian and will always appear to help their master should the need arise. When their master dies, the Gu dies alongside her.