Hi Fernando,
It seems to me that Elgood notes in his book "Arms & Armour of Arabia" that on the janbiyya scabbard, the bulb at the tip represented a garlic bulb and was termed 'thum' if memory serves. Now if that was a scabbard from out here in the west, that bulby thing would be a dead ringer for a rattler (nasty critters!)
S., thank you!
All best regards,
Jim