Final answer:
Penny referred to 'cheap cabarets' as what filled life like an explosion, epitomizing the bustling nightlife and entertainment options of urban cities during her era.
Step-by-step explanation:
According to Penny, it was cheap cabarets that filled life like an explosion. These venues were part of the vibrant nightlife in urban cities during a time of social change and population growth. Cabarets in Paris, such as Moulin Rouge and Moulin de la Galette, were particularly popular and depicted by artists like Toulouse-Lautrec, who captured the often-tawdry atmosphere. Besides cabarets, people also frequented dance halls, where even after long workdays, they found the energy to dance. Moreover, this period saw a variety of entertainment options, including melodramas and traveling circuses, which captured audiences with their exaggerated morality plays and spectacles.