因为在三个月内，公安局连续收到两封恐吓信，没有邮寄地址，但署名都是“黑猫”。
yīnwèi zài sān ge yuè nèi ，gōng\'ānjú liánxù shōudào liǎng fēng kǒnghèxìn ，méiyǒu yóujìdìzhǐ ，dàn shǔmíng dōu shì “hēimāo ”。
In the last three months, the police station had received two successive terrorist threats. They had no addresses, but both were signed "black cat".