This page uses client-side javascript. That means your computer will be doing the thinking. Adding many words will increase the number of permutations very quickly.
Here's a way to figure it out.
Additionally, the way the form is populated with your results means that all of the data has to be stored in a string. Your computer will have to keep re-allocating memory to hold it and will probably be brought to its knees with more than seven words. Consider yourself warned.