It is extremely easy to show restraint, and does not cost anything: one could be spreading salt on those flayed alive, but a properly restrained person would abstain from doing so [not to be taken too literally, but as an example]. Any action is always restrained, because without that restraint one could be doing much more [or much worse]. It is all a matter of presentation.
And that should be Israel's answer: "Clearly we ARE showing restraint, because Gaza still exists. After a fashion."