Walt: If that's true, if you don't know who I am, then maybe your best course would be to tread lightly.
Walt purposely leaves the meaning of “tread lightly” ambiguous. It can be interpreted as asking Hank not to rush things, since just coming out and accusing Walt of cooking meth could tear their entire family apart. Or, more sinisterly, he could be warning Hank that if he really doesn’t know about the full extent of Walt’s crimes then he better not mess with him; unless he wants to end up in a barrel filled with hydrofluoric acid.
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