         for y in yOffsets
           bottomLeft = Vec.add [x, y], boundingBox[0]
           topRight   = Vec.add [x, y], boundingBox[1]
-          found = _.uniq @quad.intersecting [bottomLeft, topRight]
+          found = _.uniq @quadtree.intersecting [bottomLeft, topRight]
           for candidate in found
             continue if candidate is body
             if Utils.aabbOverlap boundingBox, candidate.aabb(), [x, y]

      contacts.push contact for contact in a.contactPoints b, [offsetX, offsetY]
    contacts

  resolveInterpenetration: (contact) ->
    contact.resolveInterpenetration()

  resolveVelocity: (contact, dt) ->
    contact.resolveVelocity dt

  constrain: (body) ->
    body.position = @constrainPosition body.position
    body

            worstSepV = sepV

        break if worstSepV > 0
        worst.resolveVelocity dt

      @paused = true if @pauseOnContact

