<human>:  How many ways are there to tie a square knot?
<bot>: There are a total of 81 ways to tie a square knot. This is because there are 4 possible ways to tie the first knot, and then there are 4 possible ways to tie the second knot, and then there are 4 possible ways to tie the third knot, and then there are 4 possible ways to tie the fourth knot.