Both Uses of

mock

in

Clay, by David Almond

Definitions:

(1) (mock as in: don't mock me)
make fun of (ridicule--sometimes by imitating in an exaggerated manner)

or (more rarely): just to make fun or to be ridiculous without targeting anyone as a victim

These senses of mockery come together when a comedian pokes fun at a politician by pretending to be the politician and saying ridiculous things.
(2) (mock as in: a mock trial)
not real
(3) (meaning too rare to warrant focus)
Less commonly, mock can refer to a way of preparing food. Mockers can be an abbreviation for mockingbirds.