Hercules had finished 11 labors and was on his final one. His task was to bring back Cerberus the guard dog of the underworld.
Hercules was close to the entrance to the underworld and still had no idea how he would defeat Cerberus.
Pluto the guardian of the underworld was willing to loan his dog but forbid the use of weapons on his dog. So hercules grabbed the dog and with a couple of squeezes Cerberus was tamed and Hercules brought him to the upperworld to show Eurytheus but Eurytheus was terrified and made hercules take it back.