Looking at the musclebound tiger genie you get a desire to be feline too. "Genie, I wish I was a cat!" you say.
"Granted!" replies the genie, pointing his paws at you.
There is a puff and in an instant you are transformed into a small black and white cat! You're no bigger than the genie's bulky footpaw! "Genie, this isn't what I wanted! I wanted to be an anthromorphic cat and the same size!"
The genie looks down and shrugs "Sorry master, but you should have said. I can rectify it, but it'll cost you another wish."