It's got me stumped. Obviously, a handle of sorts slipped into the three tangs on the back. However, if it is a saw, it would likely only cut in one direction (pushed) because the handle would slip out if pressure was applied when pulling it back.
Also, it couldn't cut very deep without hitting the handle.
I thought it might be used to clean out a small groove or something that is already cut.
Just guessing... :-\