A few from Will:
“Your brain is as dry as the remainder biscuit after voyage.”
As You Like It (Act 2, Scene 7)
“His wit’s as thick as a Tewkesbury mustard.”
Henry IV Part 2 (Act 2, Scene 4)
“More of your conversation would infect my brain.”
Coriolanus (Act 2, Scene 1)
@grayman @Susandoyle
You're the reason the Oxford English dictionary removed the word, "gullible".