Why are some parts of the body ticklish and others are not?

It depends partly on the nerve endings in those areas. The body's ticklish areas tend to be those most vulnerable to attack. The axillary vein and artery are found in the underarm, which also allows unhindered access to the heart. The neck contains the carotids, arteries that supply the brain with blood. In the feet, highly sensitive nerve receptors are located close to the skin's surface, making feet extra sensitive to a delicate touch.