Carved conch shell

Image cropped for size; from the collections of the Philadelphia Museum of Art:

This shell from the 11th century, which was probably used to hold and pour sacred water during religious ceremonies, depicts the god Vishnu who is known for using a conch shell as a war trumpet. (Bengali or Orissan)

Via A London Salmagundi.

Reposted from 2015 (!) to add some new information about Neolithic shell trumpets.  BTW, both the source and the via in the old post above have undergone linkrot over the past 10 years.  The Philadelphia Museum of Art one can probably be found with a quick search, but I'm sorry to see the blog A London Salmagundi gone; they used to post some interesting stuff.

Here are some excerpts from the abstract and discussion of an interesting article in the Cambridge University Press:

The use of large Charonia seashells as labial vibration aerophones is documented in various cultures around the world. In Catalonia, north-eastern Iberia, 12 such instruments have been recovered from Neolithic contexts, dating from the second half of the fifth and the first half of the fourth millennia BC, yet they have received little attention in academia. Given that some examples retain the ability to produce sounds, their archaeoacoustic study offers insight into possible uses and meanings for Neolithic communities. While not all can still produce sounds, the high sound intensity of those that do may indicate a primary function as signalling devices that facilitated communication in Neolithic communities...

Based on the results obtained from the acoustic testing of the eight playable shell trumpets from Neolithic Catalonia, we argue that the primary acoustic characteristic of these instruments—their most notable and likely most functional feature—is their high sound intensity, which aligns with their interpretation as signalling instruments. In this context, techniques such as bending or hand-stopping, which involve a loss of energy, may aid expression but would likely hinder the effectiveness of signalling over long distances. A similar issue applies to overtones: producing them requires more effort and technical skill, and the resulting sound tends to be weaker in terms of intensity.

Shell trumpets may have enabled long-distance communication due to their high sound pressure levels, surpassing any other known prehistoric tool in acoustic power. 

So that corresponds with the observation that Vishnu used a conch shell as a war trumpet, and provides justification for such events in movies and fantasy literature.  You learn something every day.