img.swing {
    animation: swing ease-in-out 1s infinite alternate;
    transform-origin: center -20px;
    position: relative;
    display: inline-block;
}

img.swing:after {
    content: '';
    position: absolute;
    width: 20px;
    height: 20px;
    border: 1px solid #999;
    top: -10px;
    left: 50%;
    z-index: 0;
    border-bottom: none;
    border-right: none;
    transform: rotate(45deg);
}

/* nail */
img.swing:before {
    content: '';
    position: absolute;
    width: 5px;
    height: 5px;
    top: -14px;
    left: 54%;
    z-index: 5;
    border-radius: 50% 50%;
    background: #000;
}

@keyframes swing {
    0% {
        transform: rotate(3deg);
    }
    100% {
        transform: rotate(-3deg);
    }
}