Answer:
-he knows that they cannot move the boulder blocking the doorway.-
Step-by-step explanation:
*looking at this statement he made* "if I killed him
we perished there as well, for we could never
move his ponderous doorway slab aside." (hope this helps) *he knows that they wont be able to move the boulder due to its huge size so they wait till the cyclops wakes up and move the boulder to let his sheep out and they plan on blinding him with a large spare*