It wouldn't be that hard to get it to search for the word "cloud" anywhere in the text box ignoring capitalisation, so that cloud, Cloud, clouds, a cloud or the clouds would all work. Still, it's probably too much effort for the gain needed, the best solution is probably to hide the answers behind an "I'm ready to answer" option and have a much higher penalty for failing to answer after selecting that than for admitting "I don't know".