mrdoob/three.js — pull request #650 by sirlantis (2011-10-14 16:08:23+00:00)
Title: Always use shortest path for Quaternion.slerp

Also see: http://www.euclideanspace.com/maths/algebra/realNormedAlgebra/quaternions/slerp/ Other Issues, Inverting Quaternions

EuclideanSpace didn't include it in the original example because it will reduce/collapse interpolations between a given Q1 (x-rotation: 360°) a given Q2 (x-rotation: 720°). However I recall the definition of `slerp` to always use the shortest path and expected it to behave like this.