Hiking

I went hiking with a friend yesterday around Lake Frank in Montgomery County, Md. I had a good time -- saw a turtle in the middle of a trail with an orange shell, butterflies hanging around wildflowers, and a floppy eared goat that bleated like a human being. The goat might make it into one of my poems. I bought a big bag of jelly beans in a plastic bag with the word "yum" written all around it. A few questions 1) How did "yum" become a word meaning delicious? 2) Does it work -- does it make people more likely to buy food with that word all over its wrapping?