Their physical abilities are exactly the same: None
The fact that you look like an animal doesn' t mean you are actually an animal now. Polymorph spells dont change your type or grant abilities not listed under the spell or the general rules for polymorph.
Beast Shape says:
When you cast this spell, you can assume the form of any Small or Medium creature of the animal type. If the form you assume has any of the following abilities, you gain the listed ability: climb 30 feet, fly 30 feet (average maneuverability), swim 30 feet, darkvision 60 feet, low-light vision, and scent.
Small animal: If the form you take is that of a Small animal, you gain a +2 size bonus to your Dexterity and a +1 natural armor bonus.
Medium animal: If the form you take is that of a Medium animal, you gain a +2 size bonus to your Strength and a +2 natural armor bonus.
As you can see, it doesn't grant you a strength, dexterity or constitution scores, so if you are a creature without those scores (and that's different from having 0 on those scores), you cannot even increase them.
A character with a Strength score of 0 is too weak to move in any way and is unconscious.
Some creatures (such as incorporeal creatures) do not possess a Strength score and have no modifier at all to Strength-based skills or checks.
A zombie that is affected by Bear's Endurance won't gain +4 constitution, nor they will become an intelligent undead if you cast Eagle's Splendor (+4 intelligence), because they don't have that ability score at all.
For an ability score to be increased, it first requires to have an score (and even 0 is enough here). For instance, the Impart Mind spell does exactly that, it grants mental scores to a target that normally doesn't have those scores: objects.