A friend's sketchbook

Question

I was going through some old sketchbooks with a friend when I found this page:

I'm not sure what it could mean, but I seem to recall that this friend of mine loved making puzzles.

Hint:

One last comment: this friend historically used vigenere variants in his puzzles.

Hint 2:

Despite the previous hint, the knowledge tag is not needed for this puzzle.

Hint 3:

Daniel S was on the right track, but a couple of pieces of text need to be extracted from the image (steganography is not required)

Answer 1

It might be

SACRED COWS

The images all appear to be

figures of speech with the correct animal appearing in the next picture.

Thus

I. Raining cats and dogs II-III. Hold you horses IV. Cat got your tongue V. Dance monkey VI. Bird brained VII. Make a beeline for the exit VIII. Ants in your pants IX. Straw that broke the camel’s back X. Butterflies in the stomach XI. Sacred cows (assuming wrap around)

Answer 2

As noted by Daniel S:

The images all appear to be

figures of speech with the correct animal appearing in the next picture.

Going off of the answer, we have (for a partial answer):

I. Raining cats and dogs. (animals falling from the sky, used to represent when it is raining really hard)

II-III. Hold your horses. (stop what you're doing. There might be another animal idiom involving horses that would relate to this, but I can't think of it.)

IV. Cat got your tongue (unable to talk due to nervousness)

V. Dance monkey (acting foolishly for the entertainment of others)

VI. Killing two birds with one stone (getting 2 things done at once)

VII. Make a beeline for the exit (go to the exit)

VIII. Ants in your pants (acting very jittery?)

IX. Straw that broke the camel's back (Wasting a last chance to do something)

X. Butterflies in the stomach (being homesick?)

XI. Holy cow (very impressive)

So it might be

Holy cow (since it would be very impressive if someone solved it correctly)

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_{This answer is based off of Daniel S' answer and 0x5453's comment}