We don't post jokes on TMZ, but this one is so frickin' hilarious we made an exception.
Bill Maher was on his game per usual Friday night, and he riffed on a story about a school kid's science project designed to answer the question ... "Does your cat's butthole really touch all the surfaces in your home?"
Kaeden Griffin, a 6th grader from Tennessee, and his mom -- who was homeschooling the boy -- decided to crack the case by putting red lipstick on the buttholes of their 2 felines. The cats went here and there in the house and mother and son chronicled their results.
In case you're wondering ... long and medium-haired cats made no butthole contact with soft or hard surfaces, but the buttholes of short-haired cats never touched hard services. Sounds like a smear campaign if you ask us.
Anyway ... Bill's take on 'Real Time' is just hysterical. Watch and laugh your ass off.
It's certainly a cautionary tale for the Bidens, who are in the process of adopting a cat.