Harold is a fearless badass. :)
With just a dive knife? Even if you hit it in the really small brain tiger sharks have they will still try to bite you due to nerves still reacting. Also tiger sharks are one of the most aggressive sharks, the other two being makos and bull sharks. Bull sharks, while smaller, will go after anything it thinks is food. The novel Jaws, which the movie is based off of was in turn based off of several shark attacks in New York in 1916.
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Tango
If that's a tiger shark then poor Harold is going to be a fearless snack.