Answer:
He made Charlie compete with a mouse named Algernon to solve a maze.
Step-by-step explanation:
On the fourth day of the experiment, Burt who was among those administering intelligence quotient tests on Charlie made him compete with a mouse named Algernon to solve a maze puzzle which is quite complicated.
Prior to this time, the mouse had already undergone the Strauss and Nemur's experimental surgeries. The mouse passed the maze test, compared to Charlie who failed at his.