Why does gandalf ask if the cave is thoroughly checked?

Gandalf knew of the dangers they faced, and had been through the area before...... unlike his companions. Gandalf worried that the cave might house the creatures (monsters) who'd come to the area after the fight at the Mines of Moria. The dwarves believed the cave tobe empty, but as usual, Gandalf was correct, and the group soon found out the cave was home to a number of goblins, who then took them prisoner.