Shake of this character in straight-grained trees affects only one or two central boards when cut into lumber, but in spiral-grained timber the damage is much greater.

When shake consists of several radial clefts it is termed _star shake_.

In some instances one or more of these clefts may extend nearly to the bark.

In felled or converted timber clefts due to heart shake may be distinguished from seasoning cracks by the darker color of the exposed surfaces.
Such clefts, however, tend to open up more and more as the timber seasons.
_Cup_ or _ring shake_ results from the pulling apart of two or more growth rings.

It is one of the most serious defects to which sound timber is subject, as it seriously reduces the technical properties of wood.