Dogs will grab at any excuse they can find to jump, and a new person is one of the most commonly used excuses. This jumping is nothing like that in the last post; they're not doing it to get around, they're doing it because they're dogs and they do whatever the want, gosh. If you invite a new friend over for a Halo competition/wine tasting extravaganza, as you so often do, your dog will be up on them like an escaping prisoner on a fence: quick and desperate. And if they aren't, they want to be.
Because I value the accuracy of this scientifically rigorous blog, I jumped on a new person just the other day, and I can assure you from my new home in a holding cell, it is definitely something that humans can't do. At least that's what my lawyer tells me.
(flickr photo Jumping Dog outside Tate Modern by dps; http://www.flickr.com/photos/dps/357218625/)