Paper can only be recycled 3 times, because the fibers get shorter and weaker each time the paper is recycled.
Knock on wood
Knock on wood A new method for determining whether trees are
rotten inside has been developed for use in forestry. The new
method uses analysis of the sound made when a tree is hit with a
hammer to determine internal wood conditions. This is a big
improvement on the old method of actually drilling into the tree to
take a core sample. This new technique is non-invasive and so does
not damage the tree at all. 17 OCTOBER 1998, P. 21
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