The moment the rats went in, they found that there was only a single figure that was standing in the room. However, even though this figure was alone, it wasn't someone that could be underestimated.
The moment the rats went in, Brainy was able to sense the aura of the figure that was inside and it immediately made it decide to pull the rats out. It was just too bad that the figure inside didn't plan on letting them go.
Because of how small the room was, as soon as the rats entered, the figure was able to detect them.
The figure inside moved at a speed that the rats couldn't keep up to and in a flash, all the rats were being held in the figure's hand.