When they go back to Rufus' cabin, while Dean is showing Kevin around the house one of the weapons on the table is Death's hand scythe. Death took it back from Dean when they met, so the weapon shouldn't be there.
In the previous episode, the tablet is in red clay, now it appears to be in stone.
The Leviathan tablet was just encased in red clay in the last episode, not made of it, the tablet itself has always been made of stone. The tablet had been buried in the Earth for several millennia at least, the clay had just encased the tablet and hardened around it.