Location: Rail Nomads Camp, on the long North/South path through the middle of camp, a little bit to the West and South of the residence trailers (where Ralphy's Mom is)
Find a statue on the west side of the path. At level 1 Animal Whisperer, this is a 27% Hard challenge. Use the skill on the statue. If successful, a 15 HP Rat will follow the Ranger who used the skill. The statue will no longer respond to additional attempts. The Rat will also give the Secret of NIMH buff granting +1 intelligence to the Ranger, as long as the Rat is alive. The Rat is fairly weak, doing at most 10 points of damage, and the game will control it during combat. If the Rat dies, after a short time (maybe about 30 minutes), a new Rat will appear by the statue, awaiting the Animal Whisperer challenge attempt.