The slime is stored in large internal glands and forced out through the oral papillae by a squeeze of the body. High-speed filming shows the papilla tips shaking rapidly during ejection, laying the slime down in a zigzag net over a wider area than a steady jet would reach. Analysis indicates the shaking arises from the interaction between the fast jet and the elastic papilla, an instability rather than a controlled muscular flick.
The slime is mostly water with proteins and surfactant, and it stiffens on contact and drying into a stiff fibre that entangles the prey's legs. The worm then bites, injects saliva and feeds on the liquefied tissue. Slime is metabolically expensive and takes weeks to replenish, so it is not fired casually.
The animal itself is worth knowing for its position. Onychophorans are not worms in the annelid sense; they are a separate phylum, closely allied to arthropods and tardigrades, with unjointed limbs and claws. Their relationship to arthropods is well supported, but the internal branching of onychophoran groups and the number of living species remain unsettled.