Listerine active ingredients: menthol, thymol, eucalytpol, and methyl salicylate (wintergreen oil).

Eucalyptol is a cyclic ether and is toxic if ingested in higher than recommended dosages and it's an ingredient in natural bug sprays.

Thymol is a phenol and has antimicrobial and antifungal properties.

Menthol is another phenol derived from mint oils and is an analgesic.

Methyl salicylate is an ester (fancy phenol) that will dilate capillaries and increase bloodflow and is also an antiseptic--can be fatal is too much is ingested or absorbed.

I would not use it on a frog.