How to use the material components for Pass Without Trace

I am aware that many material components are either a joke (good or bad) or somehow related to how the spell works (IE: fleece for illusion is pulling the wool over someone). But for Pass Without Trace I cannot work out the connection to material components.

What is the link between the spell, and the ashes from a burned leaf of mistletoe and sprig of spruce used as the material components?

The only thing I can think of is that burning something creates smoke, which obfuscates vision, and spruce smells nice so covers scent. But I assume there is something I am missing as to why mistletoe and spruce rather than anything else smelly or burnt.

Note: I am not asking for designer reasons, but for links between the components and the spell.