My arab mare has (she now belongs to a friend of mine) one hell of a weird personality though..VERY dog like..
That wench, in her younger days could slip through the tiniest of openings to get into hay ( I swear she can army crawl:/ )..I once found her in our hay shed ON TOP of a 3 ton stack of hay just munching away....I thought she was going to kill herself on the way back down the pile, but she didnt.. She also once got out of a saddle (dont ask me how), I left her in our garden saddled so she could graze a little while I went in to eat lunch.. came back out, she had somehow gotten out of the saddle.. the girth was still cinched..I have no idea.
I could go on with the stories about this mare.. SHE IS WEIRD..
That all being said, I tend to agree with the others that MOST horses can't figure out the limping game.. UNLESS maybe you have impeccable timing on rewarding such behavior..