Visual representation of the sounds made by creatures in the game world around. The pulsating waves going out as a sphere around the creature reflecting the sounds it makes and carrying extra information:

• visibility (more or less visible) depending on the loudness of the sound or thought creature produces
• size of the sphere depending on the distance to the creature. Far creatures have tiny spheres, close ones overlap the player character going through him
• The color of pulsation reflecting the current state of the creature. Its lightness and feelings.

Visually should look reflect the importance as the secondary source of information (after visual).

As a sound wave should be visually distinguishable, but not visible at all times.

And as combined sense, creature thoughts should also produce waves.

Original idea:

Listening, seeing and feeling