"In a Brain Store" joke

A man goes to a brain store to get some brain for dinner. He sees a sign
remarking on the quality of professional brain offered at this particular brain
store. So he asks the butcher:
"How much for engineer brain?"
"4 pounds per 100g."
"How much for doctor brain?"
"6 pounds per 100g."
"How much for lawyer brain?"
"100 pounds per gram."
"100 pounds an per gram! Why is lawyer brain so expensive?"
"Do you have any idea how many lawyers you need to kill to get one gram of
brains?"