I was so nervous and I was thinking about that scream and those whistles, so I decided to go outside to have a look.

whistles 是 whistle 的复数形式，whistle 是名词，指"哨子"或"哨声"。这个词也可以作动词，表示"吹口哨"或"鸣笛"。 在这个句子中，whistles 指的是"哨子声"，即由哨子发出的声音。