Charlie Higson - "of" and "have"

I've just finished reading Charlie Higson's latest zombie book "The Sacrifice". Enjoyed it immensely but at least twice something wrangled. 

"He's got so much stuff in there, Jordan. You should of seen it"

Puffin 2012 ISBN 978-0-14133612-1

http://www.charliehigson.co.uk/

It reminded me of that famous "illusion" I use to annoy people. Put this phrase on the board for 30 seconds and ask the audience to count the "f"s. Keep reading it out. 

Finished files are the result of years of scientific study combined with the experience of years.

After the 30 seconds, remove the phrase from sight and ask the audience "How many "f"s are in the phrase?".
Most people answer 3. The answer if 6. We pronounce "of" as "ov" and so, as it doesn't sound like an "f", we ignore it. Try it. It does work.

I'd recommend the other books in Higson's series - The Enemy, The Dead and The Fear. I haven't read his "Young Bond" books yet but they're sitting invitingly on my book shelf.