A Field Guide to the Body's Odd Quirks and How Common They Really Are

This Show HN entry is an interactive web catalogue of human anatomical, neurological, and physiological oddities, each grouped by body system and paired with a rough prevalence estimate. The framing is refreshingly honest about uncertainty: rather than citing single figures, it gives ranges and admits when the data is thin or the measurement method changes the answer.

The examples span perception, structure, and reflex. Jamais vu — the inverse of déjà vu, where a familiar word or face suddenly feels alien — showed up in over half of lab subjects after they copied a word roughly 30 times, yet is thought to be rarer in daily life. Prosopagnosia (face blindness) affects an estimated 1–2.5% of people, while aphantasia leaves about 1% with no mind’s-eye imagery at all and another few percent with only faint pictures. On the physical side, it covers a permanently bent little finger (under 1%), a forearm tendon link that drags the index fingertip along when the thumb curls (present in perhaps 1 in 5, though studies scatter from 5% to 60%), and the oculocardiac reflex, where pressure on the eye slows the heart — a real hazard during eye surgery, especially in children.

The appeal is less scientific novelty than presentation: it turns scattered clinical trivia into a browsable reference with prevalence numbers attached, and it resists the temptation to overstate precision. For a technical audience it reads as a tidy example of communicating messy, range-bound data without pretending the ranges are tighter than they are.