You shouldn't laugh when someone gets hurt.
Susan is riding bikes with her boyfriend Tom, when she falls into a cactus.
Tom wants to react to Susan's fall.
Tom feels bad that Susan got hurt and rushes to help her up and pull out the thorns.
Tom feels bad that Susan got hurt but finds the situation amusing, so he bursts into laughter.
Susan thinks Tom is very sweet for rushing to her aid.
Susan see's Tom as uncaring and mean.