I love how this is made out to just happen so casually, out in the public, without Lyra thinking twice about it! Day One of relationships is pretty much that kind of awkward discovery of each other in reality, haha.
It's simple really. Our anatomy allows us to perform crazy maneuvers that other creatures could only hope to perform! Why just take a look at Princess Cadence for example from "Games Ponies Play"! [link] Obviously, her positioning on that chair would require the dislocation of the spine between the thoracic and lumbar sections of the spine, leaving her paralyzed for life! But since our anatomy says "@#$% YOU BIOLOGY!" she can perform this maneuver with ease!
That still doesn't explain why you're standing on your hindlegs...
...ugh, I'm simply preparing myself for when I arrive in the land of humans!