31. Nd1 a5
Karpov possesses a very strong sense of position in his games, which is evident in his boa-style of play. This style involves engaging with his opponents strategically, waiting for a mistake to arise, and then capitalizing on it effectively – akin to a sudden-death scenario. In this specific position, the move Knight d1 might have served as a precursor to 31…Ndf6, followed by 32. Nf2. However, by advancing the pawn to a5, Black might have acted hastily, displaying a lack of patience. It's crucial to acknowledge that, up until that juncture, Black had not committed any significant mistakes that would have led to an advantage for White. Conversely, White had maintained a strong position throughout the game. This particular position is often referred to as a "hedgehog," given that the pawn arrangement resembles the quills of a hedgehog. Given this context, the move a5 carries a considerable risk. Opting for 31…Rd8 to defend d6 or h6, thereby creating more space for the king, would have been a better course of action.