Smear frames are routinely used by artists for the expressive depiction of motion in animations. In this paper, we present an automatic, yet art-directable method for the generation of smear frames in 3D, with a focus on elongated in-betweens where an object is stretched along its trajectory. It takes as input a key-framed animation of a 3D mesh, and outputs a deformed version of this mesh for each frame of the animation, while providing for artistic refinement at the end of the animation process and prior to rendering. Our approach works in two steps. We first compute spatially and temporally coherent motion offsets that describe to which extent parts of the input mesh should be leading in front or trailing behind. We then describe a framework to stylize these motion offsets in order to produce elongated in-betweens at interactive rates, which we extend to the other two common smear frame effects: multiple in-betweens and motion lines. Novice users may rely on preset stylization functions for fast and easy prototyping, while more complex custom-made stylization functions may be designed by experienced artists through our geometry node implementation in Blender.