  The usual (type A) thin-wall Coleman-de Luccia instanton is made by a
bigger-than-half sphere of the false vacuum and a smaller-than-half sphere of
the true vacuum. It has a the standard O(4) symmetric negative mode associated
with changing the size of false vacuum region. On the other hand, the type B
instanton, made by two smaller-than-half spheres, was believed to have lost
this negative mode. We argue that such belief is misguided due to an
over-restriction on Euclidean path integral. We introduce the idea of a "purely
geometric junction" to visualize why such restriction could be removed, and
then explicitly construct this negative mode. We also show that type B and type
A instantons have the same thermal interpretation for mediating tunnelings.
