“There is a lot more juice in a grapefruit than meets the eye”

Eating a grapefruit with a spoon often results in plenty of unwelcome squirts. The joke that a grapefruit has more juice than “meets the eye” has been a popular one since at least 1931, when a quip in the Arkansas Gazette was reprinted in many other newspapers.
 
     
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19 December 1931, The Literary Digest, pg. 11:
THE reason why grapefruit continues to be popular is that there is more in it than meets the eye. — Arkansas Gazette.
 
15 December 1934, New York (NY) Times, Letters to the Editor, pg. 12:
Rather let us take a leaf from the wag who said that there is more in the grapefruit than meets the eye; let us examine all the facts before declaring that editors, as a whole, are fair-haired boys who would never pander to the lower human instincts.
JOHN M. MAHON Jr.
Harrisburg, Pa., Dec. 12, 1934.
     
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I Wish I’d Said That!:
Being a Discussion of the Art of Repartee by Two Good Listeners
By Jack Goodman and Albert Rice
New York, NY: Simon and Schuster
1935
Pg. 72:
From the pleasant comment of the unknown who remarked, when attacking and being attacked by his grapefruit, — “There’s more in this than meets the eye!”...
 
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Complete Speaker’s and Toastmaster’s Library
By Jacob Morton Braude
Published by Prentice-Hall
1965
Item notes: v.3
Pg. 35:
Grapefruit: that to which there is more than meets the eye.
 
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Esar’s Comic Dictionary
By Evan Esar
2005
Pg. 124:
grapefruit.
1. An orange with a swelled head.
2. The most frequently used American eyewash.
3. There’s more in a grapefruit than meets the eye.