Sif let out a delighted little laugh and took the dog's paw to properly shake. "He is adorable. I have no idea what the command was, or what language it was, but it seems to have worked properly! Unless that wasn't what you wanted him to do, but it's quite sweet anyway. And I don't know if his back could hold you, anyway," she added, taking in Loki's size.
So, perhaps he wasn't impressively tall, but he certainly wasn't short enough to be able to ride a dog.
"Even miniature horses can't take most humans. Carts, yes, but not weight on their backs -- have you tried a pony cart?" She was teasing, of course, eyes bright.