Even at the platinum level the [Helping Hand]s were so weak they couldn't stand up against prolonged soul sapping attacks. In fact Gordon didn't know if the clam really did have a soul attack or if the difference in power between the soul of clam and the [Helping Hand]s was extreme enough that the poor Skill Tombs just couldn't do anything but shrink and wither.
It must have been okay with the previous kills, because the [Helping Hand]s didn't have to remain continuously within the mouth of the clam. Just kill it and move on. But this time they were purposely staying longer to keep the clam from regenerating.
Knowing that any time he spent equivocating between choices was time that the [Helping Hand]s would continue to die, Gordon immediately strode up to the clam. For all intents and purposes this clam was unconscious. Perhaps it was more than unconscious, it might even be half dead or dying even at this moment. Time was of the essence.