A burp is a bodily function. It consists of a sound which stems from stomach and expelled out through the mouth with sometimes foul odor. In some countries a Burp is a complement to whoever prepared the meal. It is perfectly natural thing to occur yet some humans find it offensive. These same people might also find Body Odor offensive and wear alot of scented fragrance to cover up another naturally occuring function (In fact a humans' skin is the largest organ in its body and when this organ sweats it is expelling toxicity through the pores).
People find nature offensive, doesn't that seem Un-natural at all to anyone?
Btw, a Burp is not to be confused with a Flatulent