I did a home visit once (I used to work in the NHS in the community) to a lady who had free flying lovebirds. One of the things we were there for was to make suggestions for bits of kit that would make her safer and more independent in the kitchen so my colleague went into the kitchen to chat to her while she made some tea (she offered, we weren't testing her) while I had a conversation with her worried daughter. Tea came in and I drank mine, my colleague didn't have any but i wasn't surprised as she only ever drank coffee, then we agreed when we would come back with some kit to try and left.
Outside, my colleague said she was surprised to see me drink the tea.....because there had been bird poo in all the teacups!!! She said it was okay because the lady had carefully shaken it all out.
After that we had a code, if either of us saw anything amiss, if offered a drink we would say "no thanks I have just had one" as a signal to refuse politely.