Animal Lore is half of the pair that decides whether your pet does what you tell it. Taming gets the pet; Taming and Lore together determine how reliably it responds to a command, and Lore also feeds into how much you heal it with Veterinary. Leaving it at 100 is what causes the pet that ignores you at the worst possible moment.
This is a legendary powerscroll: it lifts the skill's ceiling from 100 to 120 for one character, permanently. The scroll is consumed on use and the cap does not transfer — you still train the skill up to the new cap yourself.
Any tamer running high-end pets wants this early, because the pets worth training are exactly the ones that punish a failed command. We also carry Animal Lore alacrity and transcendence scrolls if you are after training speed rather than a higher cap.