You can generally assume that ALL amphibians are capable secreting defensive toxins. It is one thing to feed a frog to a snake from its native range where it has 1000's of years of evolve to assimilate or detoxify the secretions, but to feed a frog from a whole other continent would be quite a risk. There is also a tremendous risk associated with the transmission of diseases/parasites to a naive predator.
Aside from that, there IS no need to feed frogs to Easterns. ALL Easterns can be converted to mice. All you need is a LIVE toad, some tuna fish, and some patience and you can convert any Eastern.
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"I know the human being and fish can coexist peacefully."
Governor George W. Bush, Jr.
"Sometimes I think the surest sign that intelligent life exists elsewhere in the universe is that none of it has tried to contact us."
Calvin and Hobbes (Scientific Progress Goes 'Boink', 1991)