We denote the *untwisted Whitehead double* of a knot $K$ to be $Wh(K)$. As an example, here is the oriented Whitehead double of the figure eight knot:

Let us look in the neighborhood of the clasp:

Through these concordances and isotopies we can ‘remove’ the clasp to get something isotopic to the unknot:

This can be done for any $K$. I know that there exist Whitehead doubles that are not smoothly slice (in fact it is conjectured that $Wh(K)$ is slice iff $K$ is), so this ‘proof’ of sliceness is obviously faulty. Since every Whitehead double has trivial Alexander Polynomial, I know this proof works for topological concordance. So my question is this: which of the 2 concordances shown above are not smooth? I cannot find any reason that a Morse function would behave in a non-smooth way at either of the above concordances in a movie of the knot.