Aiden Markram's 84 helped South Africa increase its lead to 207 runs at tea as Cameron Bancroft and the Australian team came under scrutiny for possible ball tampering in the third Test on Saturday, the latest incident in a hugely contentious series.
Markram was out just before the tea break to lift the Aussies, and South Africa ended the session 151-3 in its second innings on Day 3.
But there could be trouble ahead for opener Bancroft after he appeared to be holding a small yellow object in his hand around the time he was working on the ball as a fielder shortly before the break.
Slow-motion replays, both on TV and broadcast on the big screen at Newlands, appeared to show Bancroft then putting the small object into his underwear.
English umpires Richard Illingworth and Nigel llong did walk over and talk to Bancroft at the time, and he produced what appeared to be a black sunglasses bag from his right pocket in way of explanation.
The TV replays seemed to suggest the player had put the other small yellow object down his trousers. Although the umpires appeared satisfied with Bancroft's explanation on the field at the time and allowed play to continue, match officials could review other footage.