Journal of Archaeology in the Low Countries 1-1 (May 2009)Stijn Heeren: New views on the forfex of Virilis the veterinarian: shears, emasculator or twitch?
2 Twitch or castration clamp?

2.2 The physiology of a horse in relation to castration

In the ancient sources concerning castration mentioned above, clamping the scrotum only refers to cattle, sometimes combined with an operative procedure. In the case of equines, the scrotum is tied with a cord and castration always involves an operation. There is a good physiological reason for this. Bulls have a low hanging scrotum, which leaves ample room to place clamps. The scrotum of a stallion on the other hand is situated higher up, almost in the abdomen. There is no room to place a clamp, only to tie it with a cord to prevent the testicles moving back up into the abdomen. Since the objects under discussion were definitely used on equines (see the Aix-en-Provence altar above), the physiology of horses indicates that these objects could not have been used as castration clamps.