The slime is stored in large internal glands and forced out through paired papillae flanking the mouth. It leaves as a stream and lands as a net that hardens within seconds, pinning an insect in place. The worm then bites, injects saliva to begin digestion externally, and eats both the prey and the expensive slime.
The oscillation puzzled researchers because the papillae are far too small to house muscles fast enough. High-speed imaging and modelling published in 2015 showed the nozzle is flexible and the jet is fast, so the fluid's own momentum makes the elastic tip flap, in the same family of physics as an unattended garden hose. Frequencies reported are in the tens of hertz, and the resulting spray covers an area far larger than an aimed stream would.
Onychophorans are not worms and not arthropods, but a distinct phylum with claw-tipped legs and a body plan recognisable in Cambrian fossils. How the slime hardens so quickly, and how the proteins can reportedly be recycled from set slime back into solution, is still an active question in materials research.