Muscle contractions (also called darting) can be described as the experience of involuntary movements, jerking motions, contractions, and shaking of the limbs. These types of movements are often spontaneous but can also feel as if they are intrinsically structured around the person's current thought patterns and sensory input.
Muscle contractions are generally considered benign and can occur irrespective of any drug use, but the term "darting" was used by Alexander Shulgin to specifically describe these muscular contractions when occurring during the effects of a psychoactive substance. The term was coined by Shulgin in the book PiHKAL ("Phenethylamines I Have Known and Loved"). It is defined in the glossary as "a sudden and unexpected neurological firing that produces a momentary contraction of the musculature."
Muscle contractions are often accompanied by other coinciding effects such as ego death, machinescapes, and geometry. They most commonly induced under the influence of heavy dosages of psychedelic compounds, such as LSD, psilocybin, and mescaline.
- 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