Snappy dog

[blueST]

We have recently got a 3 year old rescue dog to accompany our existing 5 year old basset. His history is not well known, he is very thin, but apart from timidness/wariness towards strangers has been good. However today he bared his teeth and snapped at both of us when we tried to move him off the bed. The dogs are not normally allowed in the bedroom, and he has never bben on the bed before, but he squeezed past when i was carrying some drinks, hopped on the bed and made himself comfy. When I went move him off he showed his teeth and moved to snap at me and did the same to my wife. In other situations he is has always been very compliant. I have never had a dog with any aggressive tendency before, so need to find out how to address this quickly before it happens again.

Obviously, I'll be all over google looking for tips, but if you have anyhting useful to share I'd be greatful to hear it.