A piece of rope is lying on the table. How would you tie a knot in it by picking up its two ends and not letting go of them?
Tie a knot using your arms first before picking up both ends, one end in each hand. Then untie your arms, and the knot appears in the rope.
To tie a knot in your arms, first cross one arm over the other, then tuck the hand on the upper arm under the lower. From that position grab both ends of the rope and then unravel your arms.