And make sure there are sick bags handy
Incredibly valuable advice! I picked up a few before taking anyone for a flight after getting my PPL and tucked them into the back of my kneeboard. The first few people I took up were absolutely fine, and I almost forgot they were there.
Then, one afternoon, I took a friend up. It was CAVOK, the air was cool and the wind was light. We were about half an hour away from the field when I noticed he'd stopped talking. I looked across at him and saw that his skin had taken on a green hue and a rather disturbing clammy sheen. I asked him to move the headset microphone away from his mouth, and handed him a sick bag. I headed straight back to Shoreham, but by the time we got there he'd pretty much filled the bag. There was nothing else in the aircraft we could have used - that bag saved the day.
I felt terrible after the flight - Talking about it afterwards, my friend said that the sickness had started when he looked behind at the runway on the climbout. He hoped it would just go away, so he didn't mention it, but I suspected that he'd thought he would spoil the fun by asking me to turn back. Of course I would have much rather have returned early with him having enjoyed the flight, than spent the last half of the flight feeling guilty I hadn't noticed my passenger wasn't feeling well earlier!
Joel.