My dogs would have heard someone come into the house before i did, and gotten up to go investigate.
So Mr. G does that, sees its only Jason. Jason shuts him in the garage.
Just a thought
If that were the case, Meredith came in through the garage, wouldn't she have heard/seen him there? And if Jason left him back in the house *after* he was done murdering Michelle, wouldn't Mr.G. have gone back upstairs to his bed, as per his usual practice. I read/heard somewhere that Jason said Mr. G. always went up to bed when he was tired, not waiting for them to retire to the bedroom. Mr. G. 'took himself to his bed' when he was tired and ready to settle down for the night.
JMO, but I think Mr. G. was whimpering and frightened because he knew the person who came into the house that night. That's why he didn't go back upstairs to his bed. He was confused, frightened. Only his 'pack members' were in the house that night, no strangers.
My dogs too, would have heard someone coming in. Had it been a stranger, my dogs would have become extremely loud, vocal, barking and growling, etc. And I have no doubt in my mind, my extremely sweet, big dogs, would have bitten a stranger. My dogs who have grown up around children, and have never bitten anyone, have snapped at a couple strange men over the years, who they thought seemed dangerous for what ever reason. They've put themselves between me and a stranger, and if that stranger moved towards me, they have snapped. If that stranger attempted to come into our house uninvited, or made some sort of move that appeared to them as 'not right', they've reacted. When I am out walking them, and someone comes forward to pet them, they are extremely sweet dogs, accepting of pets from strangers as long as I speak and make sounds that are observed by them to be *friendly* gestures. But I have no doubt, were someone to approach me in a way that elicited fear or anger or something from me, my dogs would react in kind.