Seeing is the way G-d creates reality. Man is created in the image of G-d. This is what the spies did. They projected their own fears onto reality and made their nightmare world into reality. They misused the power of sight.
Crabs have compound eyes consisting of several thousand optical units.
The crab perceives reality through thousands of different channels. Reality is fragmented into thousands of individual pictures. The crab's eyes are on stalks which can be lowered for protection into sockets on the carapace. In other words, the crab can retract its power of sight. It can withdraw from the world of what exists and confine its sight to a dark interior world.