Manual pressure on the bulged end forces the opposite end out or the same end will spring out with release of pressure. If both ends bulge out but only one will remain flat when pressed, the can is a springer. Springers result from a moderate positive pressure in the can. Both ends of the can are bulged. Neither will remain flat without pressure.
Soft swells yield to manual pressure, but no impression can be made manually on hard swells.
Swells result from positive pressure in the can usually because of spoilage of the contents. A copy of the defect action level is attached. If any subsample contains more than 3 rodent hairs. Cocoa Powder, Press Cake Insect filth - Average exceeds 75 microscopic insect fragments per subsample of 50 grams. OR Any 1 subsample conatins more than 125 microscopic insect fragments.