Well, because they're complementary with respect to one another. And if we somehow allow them to reconnect and then we use a special type of enzyme to reform these bonds right over here, these sticky ends, because they're complementary, they're going to stick right back together. Now, when scientists discover this, they realize that one important application of restriction enzymes will be to form recombinant DNA molecules. So remember, a recombinant DNA molecule is a DNA molecule that consists of two or more different DNA sequences, DNA molecules. So to see what we mean by that, let's take a look at the following diagram. So let's suppose we have two different DNA molecules.