“Cannot run ssh”

I was trying to do a git clone on my server the other day. The problem was that I got this error:
error: cannot run ssh: No such file or directory
fatal: unable to fork
As you can see, the problem was that my server didn’t have ssh installed. The solution was to clone via http instead.
git clone git@github.com:stefanledin/bigfoot.git didn’t work, but this did:
git clone https://github.com/stefanledin/bigfoot.git