Hey! This card and the rules have had a slight reword in the newest version (which will be uploaded soon).
Rule text:
3. Take stock Your heroes prepare for the next challenge. You draw cards (usually 1) from the draw deck to replenish your hand so that it contains a minimum of 3 cards.
Card text:
Rat King Your minimum hand size is 2 when you take stock
It means that when you enter the take stock stage, you only draw a card if you have fewer than 2 cards in hand.