“appetite.” The Hebrew word is nephesh (#05315 נָ֫פֶשׁ), which has many meanings. The basic meaning is soul, the life of the person or animal. It is used as “soul,” or “person,” or the products of the soul such as appetites, emotions, passions, or desires. A good Hebrew lexicon will give a full meaning of nephesh.
[For more on “soul”, see Appendix 7, “Usages of ‘Soul.’”]
“labors…urges.” The Hebrew has both of these verbs in the past tense. The idea is that the appetite has, and continues to, urge people on to work.
“mouth.” The word “mouth” here is a metonymy for “hunger,” but “mouth” makes the point very graphically.