Sebastian consults an expert, and then ignores them

Here's a description of the contestant's attempt. Someone's probably working on collecting some images to illustrate it.

Sebastian calls a doctor who has performed an autopsy, for some insight. She tells him that a brain weighs approximately 1kg, a skull weighs about 1kg, and the muscles in the head may also weigh about 1kg. However, Sebastian decides that Mark's head is clearly bigger than average, and so guesses that his head and feet together must weigh 7.5kg. He earns second place in the task.

(Written by Karl Craven)