These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Tear Jerker: The scene where Kat read the poem at the top of the main page in class. More specifically it was meant for Patrick. Kat starts to get tears in her eyes and cries as she's reading, and the camera goes to Patrick (Heath Ledger) and you see he got kind of upset too.
That would be because the script didn't call for tears, but she actually started crying anyway. Most likely, that was also Heath's reaction to seeing her cry.