Servomechanisms were mechanical creatures that served Shardik. Like the Guardians, they each have a small radar dish coming out of their heads. After Shardik's destruction the ka-tet came across five of them walking in a circle.
These were: Rat, Snake, something resembling a truck, and a bat. The rat almost attacked Susannah Dean, but Eddie shoots the rat with the last bullet he has. As he is yelling at Roland for not killing the rat , Eddie almost froze and wanted Roland to do it, a bat comes flying out from the trees behind Eddie. Roland yells at Eddie to get down and to Eddies amazement at Roland's speed Roland shoots the bat before it can take the top of Eddies head off,