What are causes of testicular torsion?

Bell-clapper testis. Some men have a testis that hangs loosely within the tunica vaginalis which is membrane around testis. Torsion can occur if the membrane is attached unusually high on the spermatic cord, often with a testicle which lies transversely rather than vertically. Testicle thus hangs like the clapper of a bell. Additionally, contraction of the cremaster muscle can then cause testicle to twist on it's cord.