I'm going to focus on a fun runner. The line first appears on 16:

ALBERTO

Piacere, Girolamo Trombetta.

(off Luca’s bafflement)

It’s a human thing. I’m kind of an

expert.

Here Alberto uses the line to impress Luca that he (Alberto) knows a lot about the human world.

It appears again on 90:

Luca, overjoyed, takes Giulia's hand--and shows her the handshake that Alberto taught him.

LUCA

Piacere, Girolamo Trombetta.

Here, Luca "takes over" the phrase. This and the fact Luca uses it to increase his connection with Giula angers Alberto. In fact, this line of scene description follows Luca's dialogue:

Alberto, watching this betrayal, FUMES.

It is a key moment in the end of Act Two development where Alberto and Luca fight, and end up splitting up.

The third use of the line occurs on 118, right at the very end of the script:

Luca stands on the steps of the train, and does one last handshake with Alberto.

ALBERTO

Piacere, Girolamo--

Trombetta.

LUCA

Seriously, what does that mean?

ALBERTO

No idea.

Go find out for me, will ya?

Here the usage seals the friendship between Luca and Alberto while providing a bit of comedic relief: As it turns out, Alberto had no idea what the Italian words meant. His final line is a way of Alberto not only acknowledging he sometimes spewed "knowledge" based on nothing more than his imagination and he has come to accept the fact that Luca needs to head off to school to follow his curiosity and thirst for learning.

I love the use of runners. This example shows how they can reflect characters in their evolving states of being.