When did Kastro dirty himself with blood?

Question

In episode 32 of Hunter x Hunter (2011), “A x Surprising x Win”, Hisoka can distinguish Kastro from his double because the original (left) had a blood stain on his chest that was not reproduced by the double-creation technique.

But when did he acquire it? I can’t find the moment in which he would have gotten the stain. It just appears when it’s convenient to the plot.

Answer 1

According to the manga (chapter 54), that wasn’t blood, but “grime that builds up during combat”. So in the anime it was probably a case of the animators not wanting to waste time and resources on representing that before it was needed.