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?

2.1 The Aix-en-Provence altar

The scene to the right of the altar (Fig. 2) shows a man holding the bent leg of a horse, possibly a farrier trimming the hoof.[1]The scene to the left shows the clipping of the mane. There is no reference to castration found in the picture at all. If the object shown was used for castration, the person handling the horse would be depicted to the rear or beside the horses. If one accepts that the object at the centre of the altar is in any way connected to the two scenes, an interpretation of the object as a twitch is the only realistic option. One could argue that the twitching of the horse is not recognisable exactly, but at least twitching could be applied to the horses during both actions.