The rapid squirt of a proteinaceous slime jet endows velvet worms (Onychophora) with a
unique mechanism for defence from predators and for capturing prey by entangling them in a
disordered web that immobilizes their target. However, to date, neither qualitative nor
quantitative descriptions have been provided for this unique adaptation. Here we investigate
the fast oscillatory motion of the oral papillae and the exiting liquid jet that oscillates with
frequencies fB30–60 Hz. Using anatomical images, high-speed videography, theoretical
analysis and a physical simulacrum, we show that this fast oscillatory motion is the result of
an elastohydrodynamic instability driven by the interplay between the elasticity of oral
papillae and the fast unsteady flow during squirting. Our results demonstrate how passive
strategies can be cleverly harnessed by organisms, while suggesting future oscillating
microfluidic devices, as well as novel ways for micro and nanofibre production using
bioinspired strategies.