Normally you can't play 2 of the same secrets at once.
However, let's say you have freezing trap already in play, and your deck still has 1 more freezing trap and no other secrets. If your mad scientists dies and triggers the deathrattle, would it cast the additional secret or just do nothing?
Best Answer
"If the only Secret left in your deck is a copy of one you already have active, Mad Scientist will draw nothing at all."
-- Ben Brode, senior game designer on Hearthstone.