In a twitter poll asking what the arrow was pointing to in this image, only ~54% answered correctly.

The correct answer is right pleural effusion. Below illustration explains why the pleural fluid appears to be ‘beneath’ the IVC in the angle we are scanning.

Another example:

Pleural effusion (particularly the right) is often visualized from the subxiphoid window as we discussed multiple times before. Here is a nice image obtained from the same patient that shows right pleural effusion, ascites as well as mild pericardial effusion from this window.

Here is another poll testing the same concept using a different image. This time also, many people got it wrong. Anatomic correlation below.