[CentOS] Display boot menu with GRUB_TIMEOUT=0?

Hi,

On my minimal installation of CentOS 7, here's what I have in
/etc/default/grub:

GRUB_TIMEOUT=0
GRUB_DISTRIBUTOR="$(sed 's, release .*$,,g' /etc/system-release)"
GRUB_DEFAULT=saved
GRUB_DISABLE_SUBMENU=true
GRUB_TERMINAL_OUTPUT="console"
GRUB_CMDLINE_LINUX="rd.lvm.lv=centos_amandine/root \
                    rd.lvm.lv=centos_amandine/swap \
                    video=1024x768 \
                    quiet"
GRUB_DISABLE_RECOVERY="true"

According to the official documentation, pressing any alphanumerical key
just after the BIOS screen will make the GRUB menu appear. I tried that,
but to no avail.

Any idea what's the magic combination to make the GRUB boot menu appear
when GRUB_TIMEOUT is set to 0?

Cheers,

Niki
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