Consider the words sūs and sŭŭs. The former has one long u, the latter has two short ones in two syllables. For another similar pair with a different vowel, consider īmus and ĭĭmus. I wonder how easy it was for the Romans to confuse a long vowel with two short ones of the same quality, like ū vs. ŭŭ.
To make the question more concrete, I would like to know (some of) the following:
- Are there examples of word plays with ū/ŭŭ or other such combinations? I can imagine how confusing sūs and sŭŭs could make a decent joke.
- Are there misspellings that indicate that it might have been difficult to make the distinction?
- Is the distinction considered by ancient grammarians?
For me personally it is much easier to confuse ū with ŭŭ than with ŭ, although I can distinguish all three.