There are many special achievements in "Lake's Servant," and "Animal Testing" is one of them. To unlock this achievement, you need to go to the [Assist Alchemy] level, obtain the Elixir of Life there, and give one drop to the parrot.
How to Unlock the Animal Testing Achievement in Rusty Lake: Lake's Servant
Animal Testing
Animal Testing
In the [Assist Alchemy] level, after obtaining the Elixir of Life, give one drop to the parrot.
Related Guide: How to Unlock the "Idle Cat Petting" Achievement in "Lake's Servant"