git cat-file -p
Opens any object in the vault and shows what's inside.
Everything in git is one of four objects — blob, tree, commit, tag — kept in a hash-addressed vault. cat-file -p (pretty-print) opens any of them: a commit shows tree, parents, author and message; a tree lists its entries; a blob dumps its content.
It is the crypt's flashlight: half a dozen invocations — HEAD, then HEAD^{tree}, then a hash from the listing — and git's entire data model stops being an abstraction. No mystery survives a patient cat-file.
$ git cat-file -t HEAD
commit
$ git cat-file -p HEAD^{tree}
100644 blob e3c9a1f7… main.go
040000 tree 91d2f7a3… templates