A trap includes a generally U-shaped spring element with a first and a second arm extending in the same general direction, the arms ending in a set of jaws, the spring element implemented such that with the spring relaxed the jaw set is closed, a trigger linkage comprising a first link pivoted on the first arm of the spring element and a second link pivoted on the second arm of the spring element, with the first link positioned in front of the second link toward the jaw set, and pivoted to the second link at a point between the arms about equidistant from each arm, wherein the length of the links is such that, with the spring element relaxed the linkage is folded, and with the spring element arms urged apart with the arms approximately parallel, the links are essentially collinear, a constraint mechanism rigidly attached to the second link and having an extension over the first link, such that, with the spring element positioned horizontally, the linkage mechanism is constrained to a specific magnitude of folding downward, but is not constrained in folding upward except by the closing of the jaw set, and a paddle attached to an underside of one of the first link and extending toward the jaw set, the paddle having an upward curvature at an end away from the first link and closer to the jaw set.