花园里的鸟鸣声只是我们谈话的背景音。

The birds singing in the garden were just ___incidental to our conversation.

我在书店偶遇了一位老朋友——这完全是我购物行程中的意外收获。

I ran into an old friend at the bookstore—it was ___incidental to my shopping trip.

音乐会的票价包含演出费用，但停车费等杂费需要额外支付。

The concert ticket covers the performance, but ___incidental costs like parking are extra.