GEN1095 … the Gemara also says Berachos 19a “A person should never open his mouth to the Satan [i.e., the adversary –AJL].   This means that you should not say negative things. … It is [the] special power of the lips that makes a curse so damaging and so dangerous. The Gemara warns that one should not take lightly even a curse from a simpleton, and even from a non-Jew, as we see that Avimelech cursed Sarah, and the curse was fulfilled in her child, Yitzchak. Talmud, Bava Kama 93a, Megillah 15a. Avimelech gave a thousand pieces of silver to Avraham and said to Sarah [this verse]. This was a curse. Since she hid from him the fact that Avraham was her husband, and thus caused him to be afflicted, Avimelech cursed her that her children should have covered eyes. This was fulfilled when Yitzchak was older, and became blind.   CASTLE 402, 407-8