Generally, shaking happens when someone gets frustrated with a baby or small child. Usually the shaker is fed up with constant crying. Some babies cry a lot when they are hungry, wet, tired or just want company. Some infants cry at certain times. Feeding and changing them may help, but sometimes even that does not work.
Many adults enjoy tossing children in the air.
Tossing, even gentle, may be harmful and can cause major health problems later on in life. Damage from shaking may not be noticeable for years. It could show up when the child goes to school and is not able to keep up with his classmates. Not in anger, play, or for any reason. Avoid tossing of small children into the air.