Answer:
The fact that they used "stabbed" means that the thought "I shall never see this again" was deep, sudden, and bad.
"Bobbing up and down" is referred to a fishing bob that goes up and down to attract fish. Sometimes, it can be used that it is a constant reminder that, to the fisherman, the bob is always there. Perhaps "I shall never see this again" is a constant, painful reminder of the thing the narrator has lost.