Do they need to? Well, yes and no. John hadn't gotten the vibe that Ianto would be comfortable with lizard murder, though.

"Medical tape would work," he hazards, "and it would give us a chance to make sure each lizard is the right kind without fear of spitting if the stun doesn't work for some reason."

Which, you know, he doesn't expect it wouldn't but also... tape is easier than lizard murder.