"After all" is a premise indicator, "after all" is commonly used as a premise indicator rather than a conclusion indicator because it introduces reasons or evidence supporting a claim. In logical reasoning and argument structure, premises provide the basis for a conclusion and "after all" signals that what follows serves as a reason or justification for a previously stated conclusion.

I believe the correct answer just needs to weaken the argument, regardless of whether it is true or realistic in the real world. The LSAT focuses on evaluating the logic within the context of the argument presented. While the statement 'Tigers are not mammals' is factually incorrect in reality, the LSAT expects you to base your evaluation solely on the information and assumptions provided in the passage, without relying on outside knowledge or world experiences. The goal is to test whether the argument holds up logically, not its alignment with real-world facts