The perk pacifies creatures, changing their attitude toward the Vault Dweller to neutral. Neutral creatures can still be attacked, in which case they turn hostile.
Falllout 3 and Fallout: New Vegas
The perk's first rank pacifies creatures and allies them to the player with the second rank. However, allied creatures do not come to aid against other animals.
Falllout 4 and Fallout 76
For the first time in the series, the perk requires the player to actively look down their weapon's sights in order to pacify an animal. The perk comes with three ranks for both games. In Fallout 4, the first rank allows for pacification of a creature, while subsequent ranks allow for giving the creature more specific commands. In Fallout 76, each rank increases the chance to successfully pacify an animal for a short time period, with the last rank also giving a rare chance to tame the animal.
Fallout: The Roleplaying Game
The perk's first rank pacifies creatures, getting them to not roll an attack on the player. The second rank enables the pacify animals major action for the player.