From the opening chapter of One Flew Over The Cuckoo's Nest:
I creep along the wall quiet as dust in my canvas shoes, but they got special sensitive equipment detects my fear and they all look up, all three at once, eyes glittering out of the black faces like the hard glitter of radio tubes out of the back of an old radio.
Please could you explain conjugation of the verb detects? Why not detecting? Does it mean (that) detects? If so, is such a preposition omission idiomatic?