The green mystery orb is indeed a miniature watermelon! It is about the same size as a grapefruit and while it might not feed a crowd, I think it would be a pretty sweet addition to a sack lunch. I'd trade my apple for a pint sized watermelon.
This heat hasn't made watermelon growing the easiest. We had alot of marble sized melons that succumbed to the temperatures, turning black, falling off and leaving me to believe I would have a massive watermelon plant with no fruit. But Eagle Eyes spotted this little guy hiding in the shade of the zinnias, staying nice and cool (relatively). We've got one more sweetening up in the garden and hopefully more to come.