I hope you don't scare easily because today I've got a story that will make your blood run cold.

我希望你的胆子比较大，因为今天我要讲一个可怕到令人血液凝固的故事。

If you say that something makes your blood run cold or makes your blood freeze, you mean that it makes you feel very very frightened.

如果你说某事会使你的血液变冷或让你的血液冻结，你的意思是它让你感到非常非常害怕。