Identifying Errors Quiz: "The thin Francisan, understanding the Dominican smile, decided to intervene and stop the argument"

Solution 1:

The sentence looks correct as written. If you take out the dependent clause, you are left with

The thin Franciscan decided to intervene and stop the argument.

No error there. When you put the dependent phrase in, you are saying that the thin Franciscan was familiar with the particular smile and knew what to do.