Something I've noticed that Gizmo does when he's playing with dogs, or greeting children, is that he'll curl his tail up over his back like a husky, and lay his ears back (not the angry way, the submissive/friendly way). He doesn't do it when he's first greeting a dog, only if the dog initiate's play.
The tail being all curled up and slightly wagging, along with the ears being down and the big silly tongue-hanging-out grin he gets, make him look very, very puppy-like. We've nicknamed it "putting his puppy tail on". (Another thing he'll do sometimes is "put his ornery ears on". Those of you with reds will definitely know that expression.)
I think he's figured out that he looks like a friendly, adorable doggy when he does that, because he tends to put his puppy-tail on when he's around children, older folks, and anyone else who may seem a bit intimidated by him and not pet him.
He's also figured out that one of the tricks I've taught him, "sneak", will just make people melt. I really need to get it on film; it's the cutest thing I've ever trained any of my animals to do. He drops flat so his belly is flat on the ground, sticks his forelegs out in front of him, and "army-crawls" forward on his belly, one inch at a time. (Usually when he's doing it he also wags his tail wildly, completely ruining any "stealth" he might have).
Generally him sneaking is immediately met with a cute-squeal, an "Awww! Look at him! That's so cute!", an "Oh, how sweet, he's being sneaky!" or the like, and he just laps the attention up. Sneaking on his belly really has become his new way of "begging" for attention.
Another thing Gizmo absolutely adores is laughter--he gets this great big grin whenever anyone laughs, and laughs right along with them. And once a behavior makes someone laugh, he'll do it a million more times just to try and get that same response. For example, he's learned that people find him chasing his tail to be about the funniest thing ever, so he never misses an opportunity to chase his tail in front of strangers. (And if they do laugh, I have the fun of walking home with a fox who every fifteen feet will stop and spin like a top, just to see if someone will laugh at him again for it).
I had always thought that as a "wild" critter, Gizmo would be somewhat less responsive to my signals and the signals of other people. After all, dogs and cats have been selected for thousands of years for their responsiveness--a "cave dog" that was expressive and could read his master probably lived a lot longer than one that couldn't. Foxes, obviously, really haven't been bred for that (at least, not for very long), so I figured Gizmo really wouldn't read much into me other than basic body language ("angry", "friendly", "sad", etc.)
What's really amazed me with him is not only does he really seem to put a lot of effort into watching and reading people, he pays a lot of attention as to what will get him the response that he wants--in particular, he generally wants people to think he's cute, and he wants people to laugh at him. He really must consider it to be rewarding, as having someone genuinely laugh at him seems to be much more effective at rewarding a behavior than any treat I could ever give.
He's also got the most expressive face of any animal I have ever owned--dogs and cats included. With a dog or a cat, you need the ears, the posture, the tail, all of it to get the complete picture. With Gizmo, all you really need is his face to know if he's happy, angry, scared, hungry, etc. In a lot of cases, all you need are his eyes.
I just think it's amazing how an animal that's not "domestic" can match or out-do a cat or dog in so many ways; it's really taken me off-guard.