This takes place in chapter 4 room laboratory 2e. Once you gain access to the room there is a second room at the back which needs a code for access. The clue is on the computer in the 3rd email "those that remain in the nest"
For you people that just want a helping hand in the right direction to figuring out the code look here
those of you who are lazy code is in this spoiler
Once you have gone into the room turn to the right press the mechanism next to the cage with the dog in and the achievement will pop soon as the dog starts to eat.