All rush mats are [capable of becoming] tamei [with] corpse tumah, [these are] the words of R' Dosa. But the Sages say: [Rush mats can contract tumas] midras. All braided threads are tahor, except for [those] of a braided belt, these are the words of R' Dosa. But the Sages say: All [braided threads] are capable of becoming tamei, except for those of the cord used by wool dealers.