Just found a malnourished stray cat outside my house, why won’t it eat?

I found a stray cat hanging around my house today, and it’s clearly malnourished and skinny—you can feel almost all its bones when you pet it.

We tried giving it some water and milk. It drank the water but barely touched the milk. We also attempted to feed it twice, but for some reason, it just won’t eat.

Why might this be happening, and what can I do to help this cat?

Another odd thing was that it was hiding under my dad’s car, and when he started the car, the cat had no reaction at all. This was strange because my dad’s car is pretty big and loud, so it should have scared the cat, but there was practically no response. I thought it might be deaf, but it does seem to react to verbal stimuli.