WOW, didn't expect that many comments.
The old, old gentleman that I got it from said it was a "turtle hook".
One would use it to probe the "muddy" bottom of a creek or stream with the "knobbed" end to locate a "hardshell" or "snapping" turtle buried in the mud ...... and upon finding one would then use the "hook" end to get under the edge of its shell and with a quick jerk, snare the turtle and haul it out of the water.
One has to be careful around those big "snapping" turtles or they will lose a finger or two in a split second because their strike is quick n' their bite is powerful.
And the old story I was told as a kid was that if one bites hold of you that it won't let go "until it thunders".
Cheers