I see parsley listed in some cat dental treats — is that ingredient actually safe and beneficial?

Yes, parsley is a safe ingredient in cat treats. It's non-toxic and is sometimes included for its mild breath-freshening properties, similar to its use for dogs. The amount used in commercial treats is typically very small and poses no risk. However, remember that the primary benefit of dental treats comes from their mechanical chewing action, not the parsley itself. As with any treat, offer them in moderation as part of a balanced diet, and they can be a fine choice.