This depends on the skin resistance. Wet skin can have a resistance as low as 150 Ohm and dry skin may have a resistance of 15 kohm. Arms and legs have a resistance of about 100 Ohm and the trunk 200 Ohm. This implies that 110 V can cause about 160 mA to flow in the body if the skin is wet and thus be fatal. In addition skin resistance falls quickly at the point of contact, so it is important to break the contact as quickly as possible to prevent the current from rising to lethal levels.
Improper grounding can be the source of errors, noise and a lot of trouble.
Here we will focus on equipment grounding as a protection against electrical shocks. Electric instruments and appliances have equipment cases that are electrically insulated from the wires that carry the power. The isolation is provided by the insulation of the wires as shown in the figure a below. However, if the wire insulation gets damaged and makes contact to the case, the case will be at the high voltage supplied by the wires. If the user touches the instrument he or she will feel the high voltage.