The difference between the words swarmed and assembled should give you a clue as to what the answer is. Swarmed means to move somewhere in large numbers, usually crowding around something of interest to get a closer look. Assembled means to gather together in one place for a particular reason. This is usually done in an orderly fashion.
Answer: Its asking what is something that is holding him back (such as a broken leg or being not intelligent)
To hit someone
In the head slowly
