Indian stock markets opened on a cautious note on Thursday, taking a breather after a strong rally witnessed earlier in the week. The Nifty 50 index opened flat at 24,694.45, gaining 27.55 points or 0.11 per cent, while the BSE Sensex began the session at 81,354.43 with a modest rise of 23.87 points or 0.03 per cent.