O - Observant, Obedient, Odd
P - Playful, Powerful, Prickly
Q - Quick, Quiet, Quirky
R - Robust, Radiant, Resourceful
S - Strong, Swift, Slinky
T - Tiny, Tough, Territorial
U - Unpredictable, Unique, Understanding
V - Vigilant, Vocal, Valiant
W - Wild, Wily, Wondrous
X - X-traordinary, X-citing, X-otic (Note: There are not many adjectives starting with X that are commonly used to describe animals)
Y - Young, Yellow, Yearning
Z - Zany, Zippy, Zealous