If oil and grain for the grain-offering were mixed outside the wall, would that be kosher as an offering or not? It's a machloket! With verses as prooftexts for each view. Also, left-handed grain-taking, which is, again, problematic in terms of the grain-offering. Plus, the explicit mention of the left-hand in the verses about the person recovering from tzara'at, and the way the rules of interpretation handle it (no pun intended).