Spline tangent is not a curve tangent type. Good timing, spacing, and silhouette all lead to better poses. A line of action indicates the primary force and direction of a pose through the character's body. To create a preview of your animation in Maya, you should create a playblast. Timing in animation refers to how long an action takes to complete. Overlapping, anticipation, spacing, and timing are all considered animation principles. The insert edge loop tool can be used to add extra faces to existing geometry. Display is not a Boolean operation type.