One important thing I should point out is that grabbers are not as important as a topic sentence. Grabbers are OPTIONAL. Students MUST have a topic sentence but they don't necessarily need a grabber. The main purpose of a beginning is to INTRODUCE THE TOPIC via the topic sentence.
Anyway, if you were writing an expository piece about your favorite animal, first you would have to think about what your favorite animal is and some ways you would describe it. Your grabber should give the reader hints on what your favorite animal is without saying what it is. You would actually say what your favorite animal is in your topic sentence which goes after your grabber. Here are some of my examples: (BLUE = grabber GREEN = topic sentence)
Snow white fluffly fur. Soft long ears. Cottonball tail. Out of all the animals in the world, I choose rabbits as my favorite animal. (Type of grabber = descriptive phrases)
The animal world wouldn't be complete without one of its most intelligent members. With a sleek, glossy body plus super fast speed, this marine mammal is simply magnificent. Let me tell you why dolphins are my favorite animal. (Type of grabber = opinion/global statement)
Rooooarrr! The "king of the jungle" announces his presence as he strides through the savannah looking over his pride and offering his protection.I'm marveled at the amazing sight of the mighty lion my most favorite animal in the entire universe. (Type of grabber = onomatopoeia)
I hope these have been of some help to you! Take care and best of luck!