Does anyone have an example of a synthetic chemical that is harmful to rats or dogs but has none on humans?

Question

I'm in a debate over the following statement by some environmentalist, which I know is wrong but can't find a clear-cut example (I would prefer the chemical is also not naturally derived, i.e. aspirin).

"There's never been a chemical found that affects animals but has no effect on humans."

Answer 1

I don't know of any. My husband is a licensed chemical applicator.

Non-chemical - a cat. Cats have been known to kill both and not harm humans ; )

Answer 2

"Never" is such a long time.  And "no" is such an uncompromising word!

I actually would tend to agree with the environmentalist because mammalian cellular metabolism is all so similar.  Nonetheless, enzyme systems do differ.  Ibuprofen and acetaminophen are toxic to dogs in doses that barely cure a headache in people.