According to Britannica, in logic?

The first example "No felines are canines" is more of a statment of the law of identity than a logical deduction. If an animal is one it can't be the other.

Perhaps the second is an issue of applying logical concept classification. It works if you are more specific.

All Crotalus (rattlesnake genus) are snakes.

Some snakes are Crotalus.

The difference is; what ever an 'individual' deduces, by the method of reasoning they employ.

These 'deductions' will only be based of the information at hand, and, can change as more details of the subject are discovered.

This is a case of 'Deductive Reasoning'.

Ditto to all of the above. I would add, defining the boundaries or origins or precise nature of things causes problems. I.e. for every statement we make we need to define it either in relation to other statements or by pointing to something in the world. The simplest of this type of thing is ultimate causation or first assumption problem. If every effect must have a cause or definition what then defines or starts the first thing? Godel 's Incompleteness "proofs" seem to me to involve this same concept.

Logic comes down to a tautological grounds. That is what Brittanica is saying. Basically, two prides, followed by a conclusion. Like,

P1 - All human beings are governed by their bellies.

P2 - Vladimar is a human being.

C - Therefore, Vladimar is governed by his belly.

And in the end, all 'thought', all 'logic', all 'reason', all '(be)causality... is imagination = ego!