Scientists discovered the atom vibrates with more regularity than the earth turns on its axis.
But that does not mean that the body "contains more heat", it means the atoms and molecules are vibrating with more energy.
This is equivalent to the assumption that all atoms vibrate independently with a frequency ν.
Any given atom will vibrate around some mean or average position within a crystalline structure, surrounded by its nearest neighbors.
That is a lower energy state, and the surplus energy makes the atoms vibrate, producing heat.
Thus the molecules and atoms which make up the human body are vibrating, colliding, and moving.
In fact the atoms in diamond can vibrate at about 40 x 10 Hz.
Several things will make the atoms in a crystal vibrate.
In the solid phase, the atoms vibrate around fixed positions.
The atoms in this part vibrate faster and are more likely to hit their neighbours.