Jun 26 - Many functions of "se"

I know that "se" in Spanish has at least 3 functions: (1) reflexive, (2) part of the passive verb construction, (3) impersonal "se"

Look at this sentence: "No creo que se sorprenda cuando escuche mi voz, pero nunca se sabe"

There are two "se" in this sentence. The first "se" I believe performs function 1 ("sorprenderse"), whereas the second "se" performs function 3 ("one never knows").

My question is: how do I know which function "se" performs when it's used? Is there any clue in the sentence that one can use?

Gracias.