Since rats can eat pretty much anything, heres a list of foods they should NOT eat. Please feel free to add something if I missed it.
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Apple seeds Apple seeds contain a small amount of cyanide.
Green bananas Inhibit starch build up
Oranges and OJ The white part on the peelings and outer layer of a peeled orange is harmful to male rats. Its OK for females
Raw brussel sprouts Fine after cooking, though
Green potato skin and eyes
Raw artichokes Inhibit protein digestion
Raw onion upset stomach tummy!
Soda Rats cant burp!
Dried Corn it has high fungal levels
Alfalfa Rats cant digest this properly.
Raw red cabbage Fine after cooking just not too much
Blue cheese Contains a toxic mold
Licorice Contains a suspected neurotoxin
Poppyseeds Toxic and can kill your rat!
Raw bulk tofu Packaged tofu is ok for eating
Raw dry beans or peanuts Beans will need to be cooked first before giving to rats.
Wild insects Well I guess these are ok cooked?