The swordsman could see where such a nail would be more likely to wound someone--particularly if it was slipped under a carpet or otherwise hidden. Unless an infiltrator was wearing oddly thick or reinforced footwear, then simply walking normally could cause crippling damage. Not that their thief had been particularly stymied by the apparent injury but the thought was there. Though... why? "Why would you own or set up something like this?"

Plus the black haired girl still seemed unable to remember her own trap-setting, maybe... "And is there someone else that could have placed the nail?"