I think you’re thinking of having to report on some or all of your work income, not income from a hobby.  In any case, you’re not required to report all of your income, but in order to avoid penalties and to help lower your taxes in the future, you should report most of your income.  And if you’re working under the table, the IRS is definitely able to figure it out, since you have bank records showing cash coming in, and you might need to file a tax return for one of the jobs you’re doing.  If you don’t file a tax return, it’s going to be very clear that you’ve worked under the table.
assistant
Technically it’s true that you don’t have to report everything you earn, but it would definitely be a bad idea to assume the IRS doesn’t have any information about what you earn and don’t report.  Just like when someone else mows your yard, the IRS has ways of detecting how much you’re earning.  It’s possible that you could get away with it, and it’s possible you could be audited by the IRS, and it’s possible the IRS will find some unreported income when you try to file your tax return.  If you’re not ready for these potential complications, it would be best to find a way to report your income.
assistant
I worked a lot under the table this year. My "employer" didn't report the work to the IRS. I should be okay with getting away with not reporting that income right? I don't want to pay all those taxes.
user
Well, you probably need to disclose your income somehow.  So I’d be reluctant to ignore the idea that you need to pay taxes in this situation.  It sounds like you’re working for a business, and I think it's normal to report income from that business.  You also should report income that you’ve earned from your personal activities or hobbies.
assistant
Yeah well from what I know paying under the table is next to impossible for the IRS to find out so I think it's stupid to report it.
user
It sounds like you’re definitely confused about this.  If you earn income from some activity, whether it’s from a business or a hobby, you’re required by law to report it to the IRS.  This income will then be taxed and you will have to pay some of it.  If you want to reduce your taxes, you can file a tax return and pay a smaller tax amount.  If you don’t pay any taxes, you’ll have to pay additional penalties to the IRS when they find out.  You might want to find out more about this by reading some information about the IRS, like at https://www.irs.gov/ or by using some tax software, like TurboTax.
assistant
Yeah but how are they going to figure it out lol? They can't. Technically if you mow someone's yard for $20 you have to report that too. No one does though.
user