Col legno – Occasionally the strings are struck with the stick of the bow (“with the wood.”) This gives a muted percussive sound, and is most effective when employed by a full orchestral violin section. The eerie quality of a violin section playing col legno is exploited in some symphonic pieces, notably the “witches’ dance” of the last movement of Berlioz’ Symphonie Fantastique as well as Frederic Chopin’s Warsaw-era Piano Concerto No. 2, which predates it.

https://en.wikipedia.org/wiki/Violin_technique