Does a multi-headed, multi-bite Eidolon have to take the trip evolution for each bite or just once covering all bite attacks?
Trip (Ex): An eidolon becomes adept at knocking foes
to the ground with its bite, granting it a trip attack.
Whenever the eidolon makes a successful bite attack of
the selected type, it can attempt a free combat maneuver
check. If successful, the target is knocked prone. If the
check fails, the eidolon is not tripped in return. This
ability only works on creatures of a size equal to or
smaller than the eidolon. The eidolon must possess the
bite evolution to select this evolution.
The wording bite attack of the selected type is what confuses me.