The Newfoundland ¹ phrase you can’t tell the mind of a squid is used of someone or something that is unreliable. The reference is to the fact that a squid moves backwards and forwards.

¹ Newfoundland is a large island off the east coast of Canada, at the mouth of the St Lawrence River. The name is reputed to have been given to the island by 15^th-century explorers. In 1949 it was united with Labrador, as Newfoundland and Labrador, to form a province of Canada.

The earliest occurrence of the phrase that I have found is from A Treasury of Newfoundland Dishes (Newfoundland: Maple Leaf Milling Company Limited, 1958), edited by Sally West, Homemakers’ Consultant at the Maple Leaf Milling Company:

“You can’t tell the mind of a squid.” This refers to an unreliable person. A squid can move backward or forward.

Among the other Newfoundland phrases mentioned in A Treasury of Newfoundland Dishes are:

– “He’s deaf as a haddock and she’s foolish as a caplin.”
– Scroopy—squeaking boots—which because they are new indicate a degree of prosperity. After a big haul of seals you “couldn’t hear your ears in church with scroopy boots.”
– “Fish in summer and fun in winter.”—everything in its place.

Some of the phrases mentioned in A Treasury of Newfoundland Dishes are not proper to Newfoundland; for example:

– “You are making a nice kettle of fish.” Making a mess of affairs.
– “You are like a fish out of water.”—Not at home in your environment.

Edward A. Stephenson, of the University of Georgia, recorded you can’t tell the mind of a squid in Some Newfoundland Phrases, Sayings, and Figures of Speech, published in American Speech: A Quarterly of Linguistic Usage (Durham, North Carolina: Duke University Press) of December 1966.

The second-earliest occurrence of the phrase that I have found is from Why Joey’s people voted Tory, by Tom Hazlitt, Toronto Star News Service, published in The Ottawa Citizen (Ottawa, Ontario) of Thursday 4^th July 1968:

In last Tuesday’s federal election, the voters of Newfoundland reversed a national trend and turfed out six of their seven Liberal members of Parliament in favor of the Tories.
And they say: “Cuz right now everybody hates Joey.”
“Joey” is Premier Joseph R. Smallwood ², staunch supporter of Prime Minister Pierre Elliott Trudeau and the most successful politician in Newfoundland history. Last year his party won 39 of the 42 seats in the provincial legislature.
So you ask, naturally: “Why should everyone suddenly hate Joey?”
And the answers come hard, fast and varied—but they add up to a trend that indicates to me that an era is over in Newfoundland, and the end is in sight for the career of Smallwood, a truly remarkable national politician.
This conclusion is modified by a couple of old Newfoundland sayings.
The first: “The older the crab, the tougher the claws.” (The premier will be 68 at Christmas.)
The second: “You can’t tell the mind of a squid”—because a squid moves backwards and forwards without warning, and so has the course of Newfoundland politics over the past few hundred years.

² A native of Newfoundland, Joseph Roberts Smallwood (1900-1991) was a Canadian politician, first Premier of Newfoundland from 1949 to 1972.

Elizabeth Kimball used the phrase to present one of the Newfoundland recipes in In from the Outports: Old-found friends from Newfoundland, published in several Canadian newspapers on Saturday 16^th July 1977—for example in The Gazette (Montreal, Quebec):

Baked Squid
“You can’t tell the mind of a squid,” has been said of an unreliable person, the squid being chosen for comparison because it can move backward or forward. The connotation does nothing, however, to lessen the popularity of Baked Squid.