DC31 versus DC31 Animal
images from manufacturer

The main difference between Dyson DC31 and DC31 Animal is:
DC31 Animal comes with a motorized brush bar that has bristles for removing animal hair and dirt from carpets whereas DC31 doesn’t.

So, DC31 Animal does a better job picking up pet hair from carpets, fabric chairs, furniture cushions, etc. If you need a hand vac for vacuuming cat and dog hair, then DC31 Animal is a better choice.

Other differences:

Weight:
DC31 Animal is heavier.
DC31 Animal weighs 3.38 lbs while DC31 weighs 2.9 lbs.

Price:
DC31 Animal is more expensive, it is priced at $269.99 while DC31 is priced at $219.99 at Dyson.com. ( prices checked on July 28, 2011 )

Color:
The color of DC31 Animal is purple while it is yellow for DC31.

The similarities between these two Dyson hand vacuum cleaners:

They both have:
Combination accessory tool and crevice tool;
Dual power mode – 10 minutes of 38 airwatts or 6 minutes of 65 airwatts;
Dyson digital motor which is smaller and lighter than conventional motors;
0.09 gallon bin and hygienic bin emptying;
Energy Star qualified battery charging system;
2 year warranty;
bagless and cordless.