Aye-ayes (Daubentonia madagascariensis) are documented percussive foragers: the thin middle finger taps wood roughly 8 times/second and the huge ears listen to the tap's decaying vibration to find beetle-larva tunnels, then the same finger gnaws in and hooks the grub out. Each tap is modelled as a damped harmonic oscillator of the local wood plug:
ωn = √(k/m) ζ = c / (2√(km))
ωd = ωn·√(1−ζ²) f = ωd / (2π)
x(t) = A·e^(−ζωn t)·sin(ωd t)
A solid plug has high stiffness k and low damping c → a high, sharp resonance. A grub cavity thins the wood shell around it, dropping k and raising c, so the tap's pitch falls and its decay speeds up — exactly the "hollow thunk" a listener can hear. The shell is thinner the closer the cavity sits to the bark, so the acoustic signature — and therefore detectability — fades with cavity depth, the same way real elastic-wave amplitude attenuates with propagation distance.
- Detection — each tap's (frequency, damping) pair is compared to the solid-wood baseline; the deviation, plus measurement noise, becomes a confidence score checked against the sensitivity threshold.
- Cavity density — how much of the branch actually holds grub tunnels (sets how many hits are even possible).
- Detection sensitivity — a lower confidence bar catches more real grubs but also more noise-triggered false alarms.
- Finger reach depth — even a correctly detected grub is only extracted if the finger's reach is at least as deep as the tunnel.