What you Need
What to do
You want to interleave the two books together about 4-5 pages at a time. The quickest way to do this is like a riffle shuffle. When you have fully interleaved the books push them together so there is an overlap of about 2-3cm. The hold the two books by their spines and try to pull them apart.
What may happen
You should find that however hard you try you won't be able to pull them apart.
Why does it happen?
All that is holding the two books together is friction. This is the same force that acts to stop you sliding a book across a table.
When you interleave the two books there is a small force pulling the two books together created by the spine of the book.
This compressive force will create a frictional force between every place the pages are interleaved, if there are 50 interleavings a small frictional force will be multiplied by 50 to create a huge force that you can't overcome with pure muscle.
The same principle is used in woodworking If you want to join two pieces of wood and you just glue them together the glue would have to be incredibly strong, but if you interleave them in a box joint lots of relatively weak glue joints will add up to produce a strong joint overall.