Fact surrogate key as foreign key in another fact table

Hi,
Kimball mentioned that "an FSK can become a foreign key in a fact table at a lower grain" in the article "Exploit Your Fact Tables" (last sentence)http://www.kimballgroup.com/2009/01/29/exploit-your-fact-tables/.
Does it mean that, Fact surrogate keys can be included in another fact table as foreign key which are at lower grain? But my understanding is, Star schema consists of single fact table surrounded by only dimensions.

You are right, this is not a common design strategy. The one thing you find after you've been reading the Kimball Group publications is that they rarely forbid anything. If it works for you, then by all means use it! If you look at their other use mentioned in that same article, "Because FSKs are assigned sequentially, a load job inserting new records will have FSKs in a contiguous range". This is a terrible idea in my opinion. Now, my SK has gone from "dumb", i.e. just provide row uniqueness to "smart", i.e. provide uniqueness as well as tell me what order the rows were loaded. There are better ways to track the ETL process that loaded a table.