  We study experimentally statistical properties of the opening times of knots
in vertically vibrated granular chains. Our measurements are in good
qualitative and quantitative agreement with a theoretical model involving three
random walks interacting via hard core exclusion in one spatial dimension. In
particular, the knot survival probability follows a universal scaling function
which is independent of the chain length, with a corresponding diffusive
characteristic time scale. Both the large-exit-time and the small-exit-time
tails of the distribution are suppressed exponentially, and the corresponding
decay coefficients are in excellent agreement with the theoretical values.
