Now I've noticed this in the recent arc most but also throughout the entire series, when the series wants you to feel something theres a good chance you are feeling that
from feeling sad:
All of the Flashbacks
Luffy vs. Usopp
feeling 'pumped up'
Luffy vs. Just about everyone
EDIT: almost forgot anytime when the song Surrounded is playing (Luffys official its time to fight music)
and when the show wants you to laugh your probably laughing
and i've noticed this alot in the current anime but it sure can give goosebumps
Luffy's speech to Blueno before Going Gear Second when his voice kicks deep, Kokoro's speech in the last 2 episodes and most of the Too Be Continued flashes at the end of the episodes recently.
One Piece is one of the best shows I've seen at doing this