Palpable Error
A bookmaker can cancel (void) your bet, claiming it was a palpable error (or a "palp"). This can occur when a bookmaker has made what they call "an obvious mistake", such as reversed the odds of a match or some other kind of accidental error made while quoting the odds.
Our servers filter away a lot of obvious palps, and automatically hide them for you, but in rare occasions they might get past our filtering systems. If the sure- or value bet is particularly high, this might be an indication that the risk of palpable error is higher than normal.