"Must Be"

There must be blood
Rushing to my fingertips
For my hands have ridges
Like little hills.

And the snow above -
The white, clenched knuckles -
Is a sign of restraint.
I must not let go.

There must be blood
Rushing to my brain
For my cheeks are red
Like a field of posies.

And the brook or stream -
The one trickling from my eye -
Is a sign of embarrassment.
I do not know what to say.

There must be blood
Rushing from me
For I am lightheaded - dizzy -
And you caused it.

And the red on your sleeve
Must be my blood - you've cut me.
(Maybe it's not blood at all.
But you have indeed cut me.)

still not sure about the last line.