Muscle contractions (also called darting) is an involuntary physical effect most often encountered when using stimulant phenethylamines and psychedelic tryptamines. These kinds of muscle contractions are generally considered benign and can occur irrespective of any drug use, but the term "darting" tends to be used to specifically describe these muscular contractions when occurring during the effects of a psychoactive. The term was coined by the Shulgins' in the book PiHKAL and he defined it in the glossary as "a sudden and unexpected neurological firing that produces a momentary contraction of the musculature."
- Shulgin A, Shulgin A. "Appendix B: Glossary". PIHKAL - A Chemical Love Story. 1991. pp 957-68 | https://www.erowid.org/library/books_online/pihkal/pihkal_glossary_appendix_b.shtml