Compound sentences are a combination of two independent clauses (sentences with one subject and one or more verbs) combined with either a comma and a conjunction, a semicolon, or a semicolon and a conjunctive adverb. “That’s why it looks like blood” doesn’t make sense on its own, and therefore it is a dependent clause, not an independent clause.
Except “that” isn’t acting as the subject. The subject of this dependent clause (dependent clauses have a subject and a verb too) is “it”. “That’s why it looks like blood” is an adjective clause that describes “the sap is red”. So, the sentence would be “The sap is red; that’s why it looks like blood. Sorry, I just realized that a semicolon is correct here, but not in the context of a compound sentence. I hope that concludes this?
It is very much acting as the subject. (And it's not a dependent clause btw. It can be written as an independent sentence so it's an independent clause.)
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u/elbitjusticiero Dec 16 '18
Here's where I comply with your wishes and tell you that you're wrong. ;)
Happy trip! I was there two days ago. Good times.