What was he sinking/thinking? A lesson on the Θ vs the S sound

The title says:
"That sinking feeling: Tourist watches as 4x4 disappears after getting stuck in mud on beach"



Both are hissing sounds. To make the Θ/th sound, you need to stick your tongue between your upper and lower front teeth and blow. Look in the mirror to check that the tip of your tongue is visible. You don't need to stick out your tongue for the s sound, which is louder and sharper. Sometimes there's a big difference between the two sounds--e.g. sink vs think.



So, waddaya think/sink? Was this a sinking/thinking man's car? Was he thick/sick in his mind?



A mere difference of a few thousand dollars, a wiser person might have sought/thought?