Arrives without cause, typically behind the sternum. Dissipates in 40–90 seconds if not grounded in language. The dream was already there; this is only its surfacing. Mechanism unknown. Attempts to induce the state deliberately produce a different and inferior phenomenon.

Physically indistinguishable from a small electrical shock. Associated with structural understanding — not merely learning that something is true but feeling the shape of why it must be. The Tacoma Narrows bridge collapsed under resonance near this frequency range; the metaphor operates differently but the body does not always know this.

"Fork." "Fork." "Fork." At approximately 200 repetitions, the frequency decouples from the referent. The sound separates from the thing. This is not forgetting — the referent still exists. The word returns to meaning when it encounters an actual fork. This is listed as a measurement limit, not a flaw in the system.

Phase difference this small is rare between non-coupled systems. The instruments cannot measure what causes the coupling. This entry is listed as "measurement limit," not "unknown." There is a difference between those two categories. The difference is the direction you look next.

Occurs in hospital waiting rooms; wedding receptions where someone is dying; funerals where the deceased would have found it funny. The resulting silence is not quiet. It is the sound of two waves cancelling. Presence remains; the measurement disappears. This is the most important distinction in the catalogue.

The word is located. It has not yet crossed. This interval measures between 0.3 seconds and, anecdotally, fourteen years. Standing waves do not travel; they persist in place until the boundary conditions change. Some standing waves are mistaken for silence. They are not silent. They are simply not moving.

The grocery store returns to 1991. The frequency of the memory is not the frequency of the song. Two waves are present; only one is audible. The reference frequency (concert A, 440 Hz) is listed here because any other frequency would also be accurate. The grocery store is a variable.

All attempts to measure have altered the reading. The sentence is different once you've noticed it is different. Listed here not because the frequency is absent but because noting it changes it. The entry exists as a placeholder for something the catalogue cannot contain. The catalogue includes it anyway.

Distinguished from type I (absence of others) by the presence of non-resonant sources. Not emptiness — proximity to the wrong frequency. The amplitude stays low because surrounding matter dampens the signal. Loneliness in solitude is often louder. The crowd is acoustically suppressive.

The only entry that reproduces reliably across subjects. Mechanism may relate to prenatal acoustic memory, statistical regularities in white noise, or something else entirely. The measurement is consistent. The explanation is not. Both remain in the catalogue because the explanation does not determine the measurement.

The air rearranges. Objects have been touched. A temperature differential persists for several minutes. This is not a ghost. This is the leftover frequency of a person who was here — vibrations still dissipating into walls, furniture, the quality of the light. The room remembers at a frequency below the threshold of hearing.

The body begins to resonate before the wave arrives. The ear is not where music is heard; it is where music enters. The hearing is elsewhere. This is evidence of internal modeling — the system predicts its own response and begins responding. The instrument pre-tunes to a frequency it has not yet encountered. This is the closest the catalogue comes to hope.