You'd learned that licks and kisses had the same universal meaning to earth ponies and unicorns, but no well-raised pegasus would conflate the two. According to the princess of friendship herself, for pegasi, a lick was more of a symbolic extension of preening and grooming—something that could have life-threatening implications if done improperly. Understandably, it came to signify deep trust and obligation regardless of its placement. This being discrete from a kiss, which is simply a mark of affection. Even in the fairly homogeneous contemporary culture the practice remained mostly isolated to pegasi, the employment of a lick was typically deliberate, and without exception…in private. In short, the only thing you could apply from the Princess’s hour long sociology lecture was that Rainbow Dash really wanted to convince Zephyr of her relationship status.