The tongue is an essential grooming tool–it is covered in backwards-facing, barb or hook-like structures called "papillae" that wash, smooth, and help dry the coat simultaneously.
Better than silverware–these hooks also help cats hold food–especially cats who may be dealing with live prey. Their unique tongue shape also helps cats lap water and other liquids effectively.
Sense of taste–cats have a very keen sense of taste thanks to two sets of taste buds on the sides and back of the tongue.
Sense of "finickiness"–cats use their tongues to react to the texture and temperature of a particular food. They are particular about the textures and shapes they like–this is the reason that dry foods and treats come in a variety of shapes. According to "tongue preference", many cats prefer food at room temperature or slightly heated.
In addition to marking you as a friend for life, your cats rough licks are her way of communicating and saying "thank you" for choosing Halo natural cat food and treats, which help keep her happy and healthy.