Using spider spawn eggs in a 2x2 confined space (I used hardened clay at the time), whether you rightclick on the walls or the floor, causes the spider to suffocate in the wall until it either dies or walks through the wall and out of the structure.
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Confirmed.

Is this still a concern in the current Minecraft version? If so, please update the affected versions in order to best aid Mojang ensuring bugs are still valid in the latest releases/pre-releases.

Still present in 1.6.2. Also affects horses.