  A genus-1 tangle G is an arc properly embedded in a standardly embedded solid
torus S in the 3-sphere. We say that a genus-1 tangle embeds in a knot K in S^3
if the tangle can be completed by adding an arc exterior to the solid torus to
form the knot K. We call K a closure of G. An obstruction to embedding a
genus-1 tangle G in a knot is given by torsion in the homology of branched
covers of S branched over G. We examine a particular example A of a genus-1
tangle, given by Krebes, and consider its two double-branched covers. Using
this homological obstruction, we show that any closure of A obtained via an arc
which passes through the hole of S an odd number of times must have determinant
divisible by three. A resulting corollary is that if A embeds in the unknot,
then the arc which completes A to the unknot must pass through the hole of S an
even number of times.
