Answer:
Even though
Step-by-step explanation:
"The boys always bought Liquorice Bootlaces" is already independent itself so let's leave that alone.
However, "even though they thought they were made of rat's blood" is a dependent clause, because you must add something before or after to make it a complete sentence. Why? Because of "Even though". If we remove "even though" it becomes "They thought they were made of rat's blood." This is still complete and it is an independent clause even though there are pronouns because there's a subject and predicate.