Complex sentence: While Lisa lectures the other students about global warming, Bart steals two walkie-talkies from the ranger station then places one in Lisa's backpack, and spits into the other, making it sound like she is farting.
Split into simpler sentences: While Lisa lectures the other students about global warming, Bart steals two walkie-talkies from the ranger station. He places one in Lisa's backpack, and spits into the other, making it sound like she is farting.