Most if not all, animals avoid the bitterness of alkaloids.

You were asking if there is evolutionary reason for the reaction. I am claiming that plants fight off being eaten by making poison and that animals try to avoid being poisoned by spitting it out. The only Proof I can offer, at this time, are the many nature shows I have watched over the years.

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At this rate, by Tuesday it will be Thursday; By Wednesday, it will be August and by Thursday, it will be the end of existence as we know it.
- Prof. Farnsworth.