Does your cat know he/she only has three legs?
If you look closely, you can just glimpse the left hindlimb.
The GIF animation is a tad choppy ... but what the hey?!
On a more existential level: I'm pretty sure that 3-legged cats (whether congenitally or surgically so) don't bother themselves with such matters. They make the necessary physical and mental adjustments and carry on.
One of my veterinary colleagues had a 3-legged (only one HL) cat and could move just as fast as a 4-legged one; she could also climb trees with no problem (other than resembling a furry nut hatch).
