Treatment of the second relative pronoun

Question

I'll appreciate it if a native speaker to especially American English would tell me how you feel and write.

1. This is the only word (that) I know which[that] explains the situation. (A grammar book)

2. Thus, things you typically encounter that might not usually trigger fear now do so. (This seems to be from a grammar site)

3. Note that the conjunction (the second that) is usually dropped in this structure; it must be dropped if the relative pronoun is a subject.
   This is the woman (who/that) Ann said could show us the church.
   (M. Swan, Practical English Usage, 498.15)

After reading M. Swan's, I think (1) should omit the second relative pronoun.

(2) might be correct with the second relative pronoun because the first relative clause is hard to consider as an inserted clause. This is the case of stacking of relative clause, but (1) isn't. (1) is the case with an inserted clause. Am I correct?

Answer 1

(1) The clearest and correct way to express this statement is: This is the only word I know that explains the situation. An inserted clause is one set off by commas. In that case, you would write: this is the only word, that I know, that explains the situation. Neither that could be removed in that case. (2)Again, not an inserted clause. It is an essential relative clause. The statement is correct as written.