Well ACARS stands for Aircraft Communication Addressing and Reporting System, it is basically a digital datalink system to transfer communications between the aircraft and ground. So, say you need to call up base to tell them something, instead of them having a separate frequency, you can just send it via ACARS. Does that make sense? I'm a bit sleepy..
It is actually a very useful and versatile system
So if we look at the message from his TCAS:
Quote:
Message content:-
DISP,MSG ACK,DOG IS TOASTY,,,,,,
Most likely he is saying: Dispatch, message acknowledged, dog is toasty.