Clean Energy Fuels collects and transports natural gas produced by animal waste from, among other sources, dairy farms. The stock soared 37% this past Wednesday, after rising 22% the prior week, prompting one Reddit poster to cheer: “Can you smell the cow poop and the Benjamins this morning?”

The company sells both renewable and conventional natural gas; its largest shareholder is French energy giant TotalEnergies. Beyond the chuckles and some nice thoughts about its business model, the chatter focused on the stock’s short...