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Essence of Materia Medica – page 137

Lycopodium is a remedy which displays an outer shell created in reaction to an inner state, but internally it is, weak and cowardly. Natrum mur. is strong but emotionally vulnerable to being hurt.
Sepia is closely related to Natrum mur. Particularly in children, they may be very difficult to tell apart. Sepia children are very sensitive, and much more excitable than Natrum mur. In their excitability, they can become flushed and hyperactive. In adult-hood, it is as if the Sepia patient has been broken down by this excessive excitability, becoming fatigued, mentally dulled, and apathetic, Natrum mur. feels affection but does not express it easily; Sepia fundamentally has lost it. The Sepia patient is much more likely to be malicious and cruel, almost enjoying hurting others; this would be unthinkable for Natrum mur.