"You need to learn whether a player is left or right footed... [and] what does he do in a one-on-one situation - stand me up or go around me?"
The Dutchman broke his nose in a clash with Keane at White Hart Lane last year. The accident was a painful reminder of the hazards facing keepers.
"In England you get bullied at corners a lot," he said.
"Forwards try to bang into you or stop you from going to get the ball. You have to protect yourself and use your whole body. You also need to learn when to go for the ball and when to stay."