Anyone who's at least 8 years old is invited to the University of Wisconsin-Milwaukee's Science Bag. The free shows are presented at 8 p.m. every Friday, with a 2 p.m. matinee one Sunday each month.

This month, Andy Pacheco, an associate professor of chemistry, presents "Eating Ammonia and Breathing Rust: Alien Life Forms of Earth!"

"For animals (including us), oxygen is necessary to extract chemical energy from the food they eat," says Pacheco, who will introduce the audience to some bacteria that generate energy in a much stranger way.

The Science Bag presentations are held in room 137 of the Physics Building on the UWM campus, on the corner of Kenwood Boulevard and Cramer Street.