Mad Doks carry all kinds of crude, rusty, medical paraphernalia. Most of the saws, blades and hammers they carry make perfect close combat weapons, but a special favourite is a huge steel syringe filled with a toxic goo of the Dok's own devising. A Mad Dok armed with an 'urty syringe always wounds on a 4+ regardless of the victim's Toughness. 'Urty syringes have no effect on vehicles, Tyranids, Daemons, Eldar Wraithguard or the Eldar Avatar.
'Urty Syringe
Source: Codex: Orks, p. 36