That’s the problem with The Far Side – since there isn’t an authorized online archive, copyright offenders sprout up like mushrooms.
P.S. And to be fair to Keera – when she posted that, my comment was not yet visible.
I would have guessed the caption as “Suddenly, Mr. Ed forgets his lines…”
There is a Farside Facebook group which frequently runs caption contests, if anyone is interested. (The Far Side Appreciation Society of Midvale).
Comics I Don't Understand 
I don’t think so. I think the joke is the horse giving the lion the side-eye and worrying about what happens next in this scene…
“How Mr. Ed was made to talk.”
According to “The Complete Far Side” (Vol. 3, page 178), the original caption was “How Mr. Ed was made to talk“.
What James said.
To provide online confirmation of Kilby’s comment: https://www.pinterest.com/pin/600175087815110846
That’s the problem with The Far Side – since there isn’t an authorized online archive, copyright offenders sprout up like mushrooms.
P.S. And to be fair to Keera – when she posted that, my comment was not yet visible.
I would have guessed the caption as “Suddenly, Mr. Ed forgets his lines…”
There is a Farside Facebook group which frequently runs caption contests, if anyone is interested. (The Far Side Appreciation Society of Midvale).
https://archive.org/details/farsidegallery00lars
And:
https://www.google.com/search?biw=1366&bih=637&ei=EyoIW-OlDMLxzgKL3oSYAg&q=far+side+archive&oq=There+is+a+Far+Side+Facebook+group+which+frequently+runs+caption+contests%2C+if+anyone+is+interested.+%28The+Far+Side+Appreciation+Society+of+Midvale%29.&gs_l=psy-ab.1.7.0i71k1l8.0.0.0.20768.0.0.0.0.0.0.0.0..0.0….0…1c..64.psy-ab..0.0.0….0.fN0T4XUVei0