Emphasis on different parts and context.

Pronunciation, context and most importantly most of these sentences wouldn’t be used like that. (Except for “die spinnen”, i say that probably daily)

Good question! Sometimes it’s stress but sometimes just context

Context. In the first two examples both sentences sound exactly the same, but it has never been a problem.

In some examples I‘d maybe expect stronger emphasis on the noun. ‚Sucht‘ (short u) vs ‚sucht‘ (long u) from the last example are pronounced very differently.