The cat is travelling at a relativistic speed for the stationary observer to see a reduction in the cat's length. The observed length is given by L=L0√(1-(v/c)^2) where c is the constant speed of light (about 300000kps) and v is the cat's speed. L0=10 and L=9 so √(1-(v/c)^2)=0.9.
Squaring, 1-(v/c)^2=0.81, v/c=√0.19=0.436 approx and v=0.436c, making v=130800 kps approx. This is about 471,000,000 kph. (The speed of light is more than a billion kph.)