1. A computer program product, tangibly embodied in a non-transitory machine-readable medium, the computer program product comprising instructions that, when read by a machine, operate to cause data processing apparatus to: determine a position of an avatar in a user interface; dynamically define a curved guide line to surround at least a portion of the determined position of the avatar, further comprising: determining a range of motion of an arm of the avatar, and defining the guide line within the range of motion of the arm, based on the determined range of motion of the arm; display, without obscuring the avatar, alphanumeric characters aligned with the guide line; receive a cursor-based user selection of one of the displayed alphanumeric characters; animate the arm of the avatar based on the cursor-based user selection; and highlight, based on receiving the selection, the selected alphanumeric character, further comprising: increasing a size of the selected alphanumeric character to a first extent, and increasing a size of alphanumeric characters on each side of the selected alphanumeric character to a second extent less than the first extent.