A few years ago, I had a couple squirrels trained to come into my kitchen to get their tasty treats which were layed about on the floor. If I placed a nut right next to my foot (actually touching my toe), he would come and get it. However, he wouldn't take a nut placed on top of my foot. He came right up to the foot, looked at the nut, thought it over, but decided to leave the nut alone. I guess he figured that's my nut and he shouldn't take it.
I also had blue jays coming into my sun room to get their treats. Bad idea, though, because their bird brains had a hard time differentiating between the sun room's glass panes and the open door. A couple birds flew into the glass panes, and I think one got a concussion. His singing sounded weird ever since that day.
So I stopped feeding the jays in the sun room, and never taught them to come further into the house, like the kitchen. But squirrels are very smart--and squirelly ;-)