If you annoy these crabs, you will hear the "grinding of teeth" in their bellies.
If you annoy these crabs, you will hear the "grinding of teeth" in their bellies.
An interesting source of sound

an interesting discovery I saw some time ago: if you annoy an Ocypode quadrata (a sand crab whose Chinese name I'm not sure about), you may hear the "grinding of teeth" in their bellies.

(this is the kind of crab. (Patrick Verdier/Wikipedia)

it has been observed before that threatened sand crabs rub pliers to make warning sounds, both males and females, as intruders approach. In order to make a friction sound, they need curved crab pliers to rub the comb-like structure on the right against the raised edge on the left.

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(screenshot of the paper)

but the researchers also found that sometimes crabs do not make a friction, but they also make a sound. So, in order to find the source of the sound, they took the crabs to the laboratory for observation. The researchers used props such as plastic toys and crabs to make subjects feel threatened and then recorded their reactions. With the help of X-rays, they discovered another source of friction: it comes from a structure called gastric mill. Stomach grinding can be understood as a structure of long teeth in the digestive tract, which is usually used to handle food.

the following is the video attached to the paper. The sound of friction can be heard in the first half, and the friction movement of the stomach grinding structure can be seen in the second half, which is synchronized with sound production.

this way of making sound is quite new, and it does have some advantages. Replace the friction crab pliers with the "grinding sound" in your belly, so that the pliers can be freed to do other defensive actions.