Sunk Cost Effect

This is actually a great representation of the sunk cost fallacy

It would be if the dog had a good reason to believe that it would get to the bone if it kept digging
- Exactly! I can't see how anyone can read this comic and think the dog actually thinks he'll find the bone if he keeps digging. He implicitly agrees with the other dog that the bone isn't there.
This is actually a great representation of me searching for my keys.
- Stop burying your keys underground
It's really not because he has absolutely zero expectation of actually getting a bone if he keeps digging. It actually makes no sense, and if you showed this to someone who's never heard of the Sunk Cost Fallacy and asked them to explain what it means, what are they going to say? "Um, it means you keep going when you know your wrong." Or something equally incorrect.

Here's a real world example of the sunk cost fallacy:

You saved up for months to buy two tickets to see a Broadway play for $400. You live in Maryland, and when it comes time to drive to NYC, your find your car won't start. You could only afford the tickets after months of saving, and now you have to rent a car to get the the show, and that will be another $400! "We have to do it. We can't let the $400 we spent on the tickets go to waste. We can eat rice and beans for two months."

The price of the tickets is the sunk cost. You've already spent it. It's gone. Now you have a brand new choice. You can spend $400 new dollars to go see a Broadway show. The fact that you already spent $400 is of no consequence, but humans just can't get it out of their heads that they'd be wasting that money if they don't spend even more money to go see the show. But that money is already gone! You now have an entirely different choice: spend $400 to go see a Broadway show. Or you can cut your losses and stay home.

That is the Sunk Cost Fallacy, not some dog who's too stupid to stop digging.
- That is the Sunk Cost Fallacy, not some dog who’s too stupid to stop digging.
  
  Sorry, but you are wrong. You are assuming Sunk Cost Fallacy only applies to ""throwing good money after bad". It also applies to time out of one's life. That is why it is often assigned to people who stay in relationships for longer than they should. The dog is throwing time away and refuses to waste the time he's already spent by giving up. See, that is the same as your example of spending an additional $400. Sunk Cost Fallacy applies to time as well.
  
  he has absolutely zero expectation of actually getting a bone if he keeps digging
  
  How do you know that the dog has zero expectation? You only know this because you are seeing a zoomed out view of all the panels of the comic. That is not the same view the dog has and the dog does in fact expect to find the bone if he digs just a little more.