He could hear the water in the lungs
The Dr appears to also be pushing on the chest of the deceased. This would move any water in the lungs around which the Dr would hear and therefore deduce that he died via drowning.
As I've written before, I don't watch westerns, but I just found a clip of Rango that shows the few minutes up to the above screencap. The surrounding area looks like Monument Valley, which is where John Ford is known to make his westerns. Feeling that Rango was looking to employ the well-known, I was concentrating on the John Ford/Monument Valley ...
Hmmm... Seem like you will have to be cautious as this reminds me of Mos Eisley Spaceport where you won't find a more wretched hive of scum and villainy:
In case you don't know, this is from Star Wars Episode IV: A New Hope.
Rango is an actor who has lost confidence in his abilities (“I’m a fraud”) trying to help the town find water. In this scene, the missing water, and Rango’s lost confidence are symbolically linked.
The Spirit of the West, with his large collection of Oscars, is a very successful actor who represents Rango’s full potential. The fishhook shows that people ...