By crouching near a brahmin and pressing the activate button you will push the brahmin over, causing it to go into a ragdoll state and getting back on its feet in a couple of seconds. You will not lose any Karma for doing this, nor will anyone or anything become hostile. Be warned that repeating this action may cause the brahmin to die. Even after it dies, no one becomes hostile and you do not lose Karma. You may also loot the body for brahmin steak.