Garlic at the threshold. Whole bulbs hung like a charm.

Intact garlic is inert. Crush, cut, or chew it and vacuolar alliinase meets cytosolic alliin and produces allicin — diallyl thiosulphinate — in seconds. Allicin forms disulphide bridges across thiol groups in cysteine-dependent active sites and deactivates the enzyme. The reaction is rapid, irreversible at biological temperature, and specific. The haemophage's iron-transport and cytochrome machinery is built on cysteine-thiol and iron-sulphur clusters. Allicin is a key in that lock.

Inhaled as aerosol from freshly crushed cloves, or absorbed through nasal and oral mucosa, it poisons the metabolic core. The folklore of the threshold is an operational note: crush the bulb, hang it where air moves, refresh it inside the four-hour window before allicin degrades. Whole decorative heads do nothing. The tradition that kept the distinction paid for it.