The scenario is to write a hook for an argumentative essay. The topic is "Can tigers be kept in zoos?", as they have less space in zoos compared to nature, and for other reasons they should not be kept in zoos.
In this answer, I will list one way to do this (if I think of more I will add to this or make a separate answer).
It is always good to interest your reader right off of the bat.
So, as M. A. Golding suggested, do some research on your topic first. Then, pick a fact that stands out to you.
This could be an interesting fact (such as __ was invented back in __ by accident), a quantity (such as __ people died during __), or anything that would encourage a reader to keep reading.
Once you have picked one, you can incorporate it into your first paragraph. It's also a good idea to come back to that fact during your conclusion - to create a nice rounded effect.
If the fact worked, then your reader will be intrigued/hooked and will decide to read more.
For example, if your essay's theme was "can tigers be kept in zoos", you could start by saying (depending on which side you are arguing for) either "__ number of tigers die in zoos each year, or "it's been proven that baby tigers develop better with human care" (I just made that up).
Then, in the end, you can round back by talking about the starting fact. You can also elaborate on why you chose the fact and how it was important because the reader would have read all the other info, so they would be ready for a deeper look at the fact in the conclusion.