Physiognomy

When the Fourth Doctor first examined himself in the mirror after regenerating he noted that "as for the phisiognomy... well nothing's perfect". (TV: Robot)

When the Eleven used the Crucible of Souls to grant all contemporary lifeforms in the universe the ability to regenerate, without end and without a need for change in physiognomy, he gave the Ravenous an endless supply of regeneration energy, on which to feed and multiply. (AUDIO: Day of the Master)