The rats were out there somewhere in the fields? Maybe. Antar's logic was sound. But Bob could have sworn that the squeaking noises begun from the trees behind him. They could have came from there since if they lived out in the open fields Killroy would have known from a long time ago and taken preventative measures. Like bigger fences so the rats cannot get through. So while Antar concluded the rats came from the fields, Bob assumes that they came somewhere from the wild. Not that he was going to tell Antar that. Bob will let the man take the lead far to the front and fail finding the rats nest. And if they really did find the rats nest in the end, he would be far behind enough to ditch the man and escape.
"I call Antar!" Bob quickly shouted out. Who were his choices of partners? One of the two terrified attendants who smelled worse than death and Antar who was death incarnate himself. That was a very easy choice. Bob will stick to Antar like glue and just depend on him to get through the crazy, hungry, cannibal rats. If it all ended well Antar would be able to kill all the rats for him no problem.
After everyone made their choices of partners, Bob took the trophy and put it away somewhere at the stables before they left. "This is mine" he claimed. No one would want a severed rat head anyway but you will never know what people want to steal in Sunberth. That and after all this Bob wanted something to show for it. When he tells the story of how he magnificently protected everyone from a pack of rats at the taverns, he was going to need some proof so he won't get laughed out.