Do you say "the pillow is stained with some substance" when you don't know if it is sweat, water, milk or tea, etc stained it

Question

stain 1 /steɪn/ ●○○ verb 1 [intransitive, transitive] to accidentally make a mark on something, especially one that cannot be removed, or to be marked in this way

Be careful you don’t stain the carpet.

This tablecloth stains very easily.

Her fingers were stained yellow from years of smoking.

stain with

a cowboy hat stained with dust and sweat

---

There are some stains on your pillow. It could be your child poured water or milk or sweat on the pillow, but you don't know what substance stained it.

Do you say "the pillow is stained with some substance"?

or do you use a better word instead of using "substance"?

Answer 1

That is a permissible construction.

It's a little bit more formal than you'd expect in day-to-day life, so if someone said it the implication is that they find the unknown substance disgusting, but it's perfectly acceptable English. A more informal way of saying it would be something like "The pillow's stained with something", "Something's stained the pillow," or simply "The pillow's stained". If you were writing a formal academic paper, you might write something like "The sample was stained with an unknown foreign substance".

Answer 2

You do not have to mention the substance at all. It makes you sound like a forensic scientist from Mars.

In fact, it is better to avoid the issue of the stain at all and just say that this needs to go in the laundry.

("null mentions" are a fascinating component of idiomatic usage. People from a more direct culture have often asked me how to say that in English and the answer is often: you don't under normal everyday circumstances)