question:  What are the tangler fields?
context: He was a captain of guards in Estates-General Correctional Institution—better known to its inmates as the Jug—and if he hadn't been able to detect the scent of trouble brewing a cell-block away, he would never have survived to reach his captaincy. From the moment that clans formed, specialization began—the hunters using the weapons made by the flint-chippers, the food cooked in clay pots made by the ceramists, over fire made by the shaman who guarded the sacred flame. The ultimate should be the complete segregation of each specialization—social and genetic measures to make them breed true, because the unspecialized man is an uncivilized man, or at any rate he does not advance civilization. And letting the specializations mix would produce genetic undesirables: clerk-laborer or Professional-GI misfits, for example, being only half specialized, would be good at no specialization. And the basis of this specialization society was: "The aptitude groups are the true races of mankind." Block O in Estates-General Correctional Institution was the disciplinary block, and because of the green straitjackets its inhabitants wore, it was called the Greensleeves. She was in a detachment of three unfortunates like herself, convoyed by an irritable guard, climbing the steel steps toward Block O from the floor below, when she heard the yelling. The two guards turned to see what was coming in as the three new candidates for the Greensleeves slumped to a stop at the head of the stairs. The outside guard pulled the switch that turned on the tanglefoot electronic fields that swamped the floor of the block corridor and of each individual cell. While the fields were on, you could ignore the prisoners—they simply could not move fast enough, against the electronic drag of the field, to do any harm. But it was a rule that, even in Block O, you didn't leave the tangler fields on all the time—only when the cell doors had to be opened or a prisoner's restraining garment removed. It was her first experience of a tanglefoot field.
output:  electronic fields near the floor to stop prisoners
options:  a type of uniform meant to keep the inmates secure  electronic fields in Block O that identify inmates  replacement for guards in Block O  electronic fields near the floor to stop prisoners