Mulch will examine the stone circle closely, looking to see if it's any kind of mechanism. If he doesn't find anything, he will push down on it firmly, as well as try twisting and turning it.
OOC: I get the sense people aren't reading my posts. Mulch has the lamp in his backpack, and insists on keeping it. People are going to have to reason with him to get him to pull it back out again. And he doesn't want to keep pushing the coffin. Mulch is a person who has a hard time sticking to something, except for a couple of things that can hold his attention for a long time. So first he was interested in the sarcophagus, then the chamber that popped up, and now the circles on the floor.