The upper portion (roughly the upper half), called the larynx, displays a number of discernible anatomical features. The most relevant ones for this subject are the thyroid cartilage and the cricoid cartilage. Both are rigid ring-like structures identifiable through palpation of the neck's midline. The thyroid cartilage, which is the upper one, has a prominence called Adam's apple (or laryngeal prominence), which is often visible, especially in males and AMAB (assigned male at birth, assuming it was not surgically removed).

The thyroid cartilage's prominence is an extremely important point of reference for this practice. Right above it is the thyroid membrane, while below it is the cricothyroid membrane. The thyroid membrane connects the thyroid cartilage to a small ring-like bone below the chin, called hyoid bone, which may or may not be palpable. The cricothyroid membrane, as its name suggests, connects the thyroid cartilage to the cricoid cartilage below, which is often palpable as well. These two membranes are the weakest spots along the neck's airway, making them critical spots to be aware of.

The bottom portion (below the cricoid cartilage), called the trachea (also known as "windpipe"), is a cartilaginous tube that connects the larynx above to the bronchi of the lungs below it. Its cartilaginous covering means this is not a compressible structure, i.e. you do not easily "close" it through external compression - you merely push it backwards, since the structure behind it (the esophagus) is much softer. The trachea is quite resistant, albeit flexible. It's like a hard rubber pipe, not a soft tube. Understanding this is essential, because there is a lot of fearmongering surrounding these concepts, as if one could easily obstruct the lumen (the open space inside) of the trachea through external compression. Actual trauma to this structure (seen here) generally requires higher amounts of biomechanical energy (such as from a car crash or a gun wound). Other structures adjacent to the trachea, like the vagus nerve, carotid arteries and jugular veins, are all more vulnerable and susceptible to damage upon compression (seen here). The same concept applies to compressions of the thyroid and cricoid cartilages, which will most likely push the larynx back, instead of actually collapsing it.

Cartilages such as the ones found around the larynx and the trachea are extremely resistent, considering their purpose is to protect the airways. Similarly to bones, they can also break or suffer fractures (seen here and here), but it is extremely unlikely to have such an outcome through manual compression of the neck. This means that midline compressions of the neck, assuming they are not centered at the membranes mentioned above, should be reasonably safe. It won't easily lead to asphyxiation, contrary to popular belief. In order to cause asphyxiation, all the structures around the airways of the neck must be compressed against each other with a much higher force, meaning it is very hard to cause pure asphyxiation without strangulation, except for direct compression of either the thyroid of cricothryroid membranes.

Disclaimer about autoerotic asphyxiation (AEA): trying to perform breath play by yourself is an extremely risky and life-threatening activity. We do not recommend trying it under any circumstances, as the risk of accidental death is high and there's not much to be done if something goes wrong, considering you'll be alone.