People who walk in bare feet may tread on a sharp object such as a needle (click on the x-ray to enlarge) or broken glass and present with a foreign body (FB) on the sole of the foot.
If there is any suspicion of a foreign body, an x-ray should be requested with a marker on the skin to help to localise it.
Non radio-lucent FBs may be localised by ultrasound. However a normal ultrasound does not completely exclude an FB.