This is  solid iron choker with grey hair and blood imbedded in the metal. It has  no hing or clasp.  It magically appeared on you as a curse from a which doctor of a rival clan as you cut her down on your first clan raid. You were exiled from your clan as a result of the curse. 

This is a cursed item. This is a unique item.

The collar has will cast haste and trigger rage on you twice per day if you receive a bleeding effect while in combat, which can be self inflicted. The spell ends if combat ends. You get +2 magical ac and 1 extra attack action as well as 10 feet added movement while hasted. While active you hear drums and ancient chanting that gets louder every round. After the second round of combat and each subsequent round you must save vs wisdom with a penalty equal to the number of rounds that you have been in combat. A saving throw failure casts "blind frenzy" on you and the music takes over your mind. The spell will only end if you fall unconscious, or are out of combat for 1 minute. You must use your action at the beginning of your turn to attack a creature (friend or foe) within melee reach. You use a melee weapon, if you have one, or an improvised weapon or unarmed strike if you don’t. If more than 3 targets are within reach, you perform a melee aoe attack causing max weapon damage x # of targets (sv dex).  All of your non-magical armor bonuses are negated. Your hearing is reduced and hearing perception has a modifier of -7. You will dance a war dance to the music while in this state and you will verbally echo the chants, getting louder each round.

These chants are very old and successful history check with dc 25 from a listening scholar will reveal it as very old form of Uthgardtian.

If you are killed while under the spell of this curse there is a 25% change to resurrect as a werebear after 5 rounds. There is a 30% chance you will be at full health and under the effects of the spell.