Well the issue is Bedivere could kill him right then and there.
Very few people could stop him right now in the night, given that Mithias has already blow out the lights.

As for Bedivere hiding his mood? Well Martin should have picked that up the very instant. He's being rather nice over his victory with Gabriel and thus has merely entertained Martin with speaking. However Once his bit is done, Bedivere would kill him outright as Martin did not follow his instructions in scurrying away :P