The one about avocados is ridiculous. Our cats eat food made from avocados for the last 3 years everyday.
Avocados
The avocado tree leaves, pits, fruit, and plant bark are likely all toxic. Clinical signs in dogs and cats include vomiting and diarrhea.
http://www.avodermnatural.com/Cat_Foods/index.htm
http://www.avodermnatural.com/About/why_avocados.htm
There are a number of very high end food manufacturers that are avocado based.