Which two rats died at the end of Mrs Frisby and the Rats of NIMH?

NIMH comes to put poison in the rats cave and the rats have to move out fast and destroy all of their machines. 10 rats stay behind including Justin, Arthur and Brutus. When the poison starts to go in the hole the rats run out their back door and wait. Only seven make it out of the hole. The rats run at the scientists two at a time over and over so it looks like there are many of them. One rats stumbles out the hole and faints while they are doing this. Eventually all the rats run off to Thorn Valley. Mrs. Frisby goes to look at the rat on the ground. It's Brutus. Mr. Ages is already there reviving him. Brutus says that he was by the front of the hole and got a lot of poison and stumbled, one rat pushed him out of the hole then went back for the other and died. We never find out who the rats that died were but Mrs. Frisby thinks it was Justin.