You unlock the coffin... (the dialogue tells you the items found, if any).
Your lockpick snaps (if you have one; a lockpick not required to pick the locks).
You fail to pick the lock - your fingers get numb from fumbling with the lock.
Outside Jiggig only: You fail to pick the lock - your fingers get numb from fumbling with the lock (and you get caught).
Ogre Guard: Hey thief! I's gonna teach ya!
You're knocked unconscious and dropped down a chute.
You slowly wake up in a strange place (you are in the level one basement of Jiggig).
You cannot pick the locks during combat. Thieving while under attack results in, "You're in mortal danger, thieving is the last thing on your mind."
Each time you fail and your fingers get numb, you temporarily lose 1 - 4 points of thieving ability. If your thieving drops below 20, you can't attempt to pick the lock. Failure is frequent even for players with thieving levels in the 80s, so expect thieving ability losses. Thieving ability can be restored by drinking Super restore potions.
This means that the average profit for looting 100 coffins using keys would result in &0000000000113703000000113,703 coins profit, ignoring the other rewards, since they are either untradeable or very cheap.
The ogre coffins are valued for being the source of Fayrg, Raurg, and Ourg bones, all of which yield good Prayer experience when buried.
For players at or above combat level 89, the basement of Jiggig is an acceptable place to pick the locks of the coffins. The zogres will not be aggressive to players at these levels. So, if you get caught picking locks outside Jiggig and are tossed down the chute to the basement, just work on the coffins there. You can only pick the locks of intact coffins. It is not safe even to bury zogre bones in the basement, as this results in aggressive skogres appearing after burying 4, just like the surface level of Jiggig.
Picking the locks often results in failure. It therefore does not seem any faster than using Brutal arrows to kill zogres and skogres for their automatic key drops.
Lockpicks may snap while picking the coffins.
When in the underground section of Jiggig, it is possible for all combat levels to use the coffins as safespots, making it possible to train in peace.