Abstract: A method of judging a biological state comprising using: (1) correlation and/or symmetry between Lyapunov exponent and entropy; and/or (2) Higuchi fractal dimension, wherein the Lyapunov exponent, entropy and Higuchi fractal dimension are indices that can express chaotic nature and derived from time series data of biological signals from a subject.

Abstract: A toy for pets, which is designed to encourage sedentary pets to exercise by attracting them to the chaotic movement of a movable object, is provided. The toy for animals includes a rotating unit, which is provided so as to allow the axis of rotation to be angled with respect to the vertical direction; a first rod having a base portion connected coaxially with the axis of rotation and a tip portion bent with respect to the base portion; a second rod, which is connected to the tip portion of the first rod and has enough flexibility to be deflected from the longitudinal direction; and a movable object mounted to the tip of the second rod with a string material. The movable object is moved chaotically in the vertical and horizontal directions within a three-dimensional space around the rotating unit by chaotically rotating the axis of rotation of the rotating unit in an arbitrary rotating direction.