What is the main symptom differentiating Strychnine toxicity from tetanus?

The main symptom that differentiates strychnine toxicity from tetanus is lockjaw. Strychnine poisoning typically leads to generalized muscle rigidity and spasms, but it does not cause the specific jaw locking that is characteristic of tetanus. In tetanus, the muscle spasm is accompanied by a specific spasm of the muscles of mastication, leading to difficulty in opening the mouth, also known as trismus or lockjaw.

While rigidity of the body can occur in both conditions, the distinct feature of lockjaw in tetanus provides a more definitive indication of that particular condition. Facial spasms can occur in both but are also not unique enough to differentiate the two. Fever is generally associated with infections and is not a prime symptom of either strychnine toxicity or tetanus. Thus, lockjaw serves as the crucial differentiating symptom between these two clinical presentations.