  In this work we study three topologies defined over the same set: the
hedgehog. As the name suggests, the hedgehog can be described as a set of
spines identified at a single point. Among others, we give a proof of the
Kowalsky hedgehog theorem, which asserts that every metrizable space is
embeddable into a countable cartesian power of the metric hedgehog. Besides,
the concept of collectionwise normality will characterized by means of a Tietze
type extension theorem. In particular we give a proof of the fact that
collectionwise normality is hereditary with respect to $F_{\sigma}$ sets.
