David with Goliath’s Sword

“I only have the sword of Goliath the Philistine, whom you killed in the valley of Elah,” the priest replied. “It is wrapped in a cloth behind the ephod. Take that if you want it, for there is nothing else here.”
“There is nothing like it!” David replied. “Give it to me!” 
1 Samuel 21:9

I don’t think I ever caught this before. When he fled from Saul, David brought Goliath’s sword with him into Gath, Goliath’s hometown. My initial thought would be that he took Goliath’s sword into Gath to remind the people of what he had done to their champion. After all, if he could take down Goliath, he could surely defeat the rest of them to. And he’d do it with Goliath’s sword. Pretty bold move, I would think.

Except, he doesn’t do that.

“David … was very afraid of what King Achish of Gath might do to him. So he pretended to be insane, scratching on doors and drooling down his beard.”
verses 12 & 13

Huh?

I’m confused as to why David would accept Goliath’s sword, which the people would recognize and possibly encourage an angry response from the Gathites (is that a word?) and then turn around and pretend he’s insane so they won’t do anything to him. Isn’t that like kicking a hornet’s nest and then trying to act like nothing happened?

Any insight into what’s happening here would be greatly appreciated. I mean…I know the story continues and I’m pretty sure I remember what happens. Maybe it’ll help if I read the next day’s entry.

On a different note: Wouldn’t it be fun to see Indiana Jones go after Goliath’s sword? Or maybe that’s just me.