It's the egg yolk they want! It took me ages to realise it too - until one day - Jameson woke up from his coma-like sleep when I boiled an egg, he marched straight into the kitchen and climbed up my leg - I literally had a 5 kilo cat attached to my bare leg with all claws digged into my skin. It wasn't a case of ''can I have some'' it was ''I am having your egg yolk''.
These days we give him most of our yolks anyway (often raw), as apparently it's full of cholesterol so neither me or OH wants to eat it.