Blood Blister: If you are sure it's a blood blister: thinning of a blood vessel wall could cause ballooning when the pressure goes up, then collapse when the pressure goes back down. The concern is if this blister doesn't resolve and gets cut, getting it to stop bleeding could be difficult.
This is an old British riddle from 1300-1900 AD. What is the longest and yet shortest thing in the world, The swiftest and yet the slowest, the most divisible and the most extended, The least valued and the most regretted, without which nothing can be done, Which devours everything, however small, and yet opens the life and spirit.
Longest palindromic subsequence. Not to be confused with Longest palindromic substring. The longest palindromic subsequence (LPS) problem is the problem of finding the longest subsequence of a string (a subsequence is obtained by deleting some of the characters from a string without reordering the remaining characters) which is also a palindrome. In general, the longest palindromic subsequence is not unique. For example, the string alfalfa has four palindromic subsequences of length 5: alala, afafa, alfla, and aflfa. However, it does not have any palindromic subsequences longer than five characters.