  Manipulations of a constrained object often use a non-rigid grasp that allows
the object to rotate relative to the end effector. This orientation slip
strategy is often present in natural human demonstrations, yet it is generally
overlooked in methods to identify constraints from such demonstrations. In this
paper, we present a method to model and recognize prehensile orientation slip
in human demonstrations of constrained interactions. Using only observations of
an end effector, we can detect the type of constraint, parameters of the
constraint, and orientation slip properties. Our method uses a novel
hierarchical model selection method that is informed by multiple origins of
physics-based evidence. A study with eight participants shows that orientation
slip occurs in natural demonstrations and confirms that it can be detected by
our method.
