phrase for "It happened just as you finished talking about it" I was pointing at a thundercloud and saying that lightning may strike, and my Chinese friend said a 4-syllable phrase that meant that it happened just as I finished talking about it.

Do you know this phrase?
In Cantonese, it is "話口未完" wa6 hau2 mei6 yun4. 

In Mandarin, perhaps "話還沒說完”，hua4 hai2 mei2 shuo1 wan2, but then it is five syllable, not four.