Rat and Rabbit compatibility
Rat (Zi, 子) and Rabbit (Mao, 卯): a punishment (Xing, 刑).
These are fixed relations among the twelve branches of the Chinese calendar, set out in the classic San Ming Tong Hui (三命通会), written in 1578, quoted below. They describe the signs, not two people: no classic gives a method for matching two people by their signs, so there is no score here.
What the book says
Punishment (Xing, 刑): the punishment of no propriety
Rat and Rabbit are the one pair of signs that punish each other on their own, outside any group of three.
The Rat is Water and the Rabbit Wood. Water gives birth to Wood, so the Rat is the mother and the Rabbit the child: mother and child punishing each other.
子属水，卯属木，水能生木，则子水为母，卯木为子，子母自相刑
Rat and Rabbit stand off at an angle, with no deference between them. Heedless of what makes one the other’s life, they push on to punish and harm each other. So it is called the punishment of no propriety.
子卯角立，无钦卑之道，不恤所以相生，进相刑害，故曰无礼。
Seeing a punishment, do not at once call it ill. Look whether the five elements hold a good hour, strength, the officer star, the seal, a noble spirit, virtue or blessing; with these good things to help, the punishment does no harm and is put to use instead.
凡见刑不可便以凶论，须看五行中有无吉辰、旺相、官星、印绶、责神、德福等物，有此诸吉相扶相助，刑不为害，而反为用
San Ming Tong Hui, volume 2: On the three punishments (论三刑) · source text
Their elements
The Rat is Water and the Rabbit is Wood: Water feeds Wood.
How much it counts
A sign is one character of the eight in a BaZi chart, the year’s branch. The book reads these relations between the pillars of one chart, and tells the reader to look at the whole chart’s elements first:
Clash and break, three harmony and six harmony: where a chart has them, ask next how its five elements get on. Misfortune may give rise to blessing, and blessing to misfortune.
相冲相破，三合六合，命中有之，即求五行相得何如。或祸中生福，福中生祸
San Ming Tong Hui, volume 3: On the symbolic stars as a whole (总论诸神煞) · source text
Birth years, and 2027
- Rat: 1924, 1936, 1948, 1960, 1972, 1984, 1996, 2008, 2020. In 2027, the Year of the Fire Goat (Ding Wei, 丁未), the Rat harms the year (Hai Tai Sui, 害太岁).
- Rabbit: 1927, 1939, 1951, 1963, 1975, 1987, 1999, 2011, 2023. In 2027, the Year of the Fire Goat (Ding Wei, 丁未), the Rabbit is in harmony with the year (San He, 三合).
A sign’s year is usually counted from Chinese New Year, between late January and mid-February; BaZi counts it from the Start of Spring, about 4 February. Born in January or early February? You may be the sign before: the sign pages check your date.
Two real people?
Each person’s chart has eight characters, and the same relations run between all of them, not only the two signs. The two-chart page sets both charts side by side, branch by branch, and gives what each chart says about marriage on its own. No score there either.
Rat with the other signs: Rat · Ox · Tiger · Dragon · Snake · Horse · Goat · Monkey · Rooster · Dog · Pig.
Rabbit with the other signs: Ox · Tiger · Rabbit · Dragon · Snake · Horse · Goat · Monkey · Rooster · Dog · Pig.