Should I add a comma before 'though' in the following case?

The dog was lying on his side. He wasn’t resting though, of that I was sure. He was dead.

Should I add a comma in the bolded sentence?

The dog was lying on his side. He wasn’t resting, though, of that I was sure. He was dead.

Solution 1:

Yes: when you use though to qualify the preceding sentence or clause as "contrary to expectation", though is parenthetical, and so it needs to be separated from the sentence by commas.

If after though you were to continue the sentence, you would need a comma after though, too, because parenthesis is marked by stops at both ends.

However, in your sentence, the comma after though introduces a comma splice, which is generally not recommended. You have two complete sentences with a subject and a finite verb: he wasn't resting and I was sure. In most cases, you cannot connect two complete sentences with a mere comma: you need a semicolon, a conjunction, a relative pronoun, or a dash (which signifies an anacoluthon, a break of syntax). Using a comma instead results in a comma splice, although there are exceptions, such as enumerations. In this case, you could use a semicolon, or possibly an m-dash (a longer dash).

The dog was lying on his side. He wasn’t resting, though; of that I was sure. He was dead.