A glass full of pee

This morning I went into my bathroom after the kids left for school and my empty water glass had mysteriously filled itself with a yellow liquid. Despite my utter disbelief, a quick sniff confirmed that this was really and truly somebody's urine. Knowing that it was most likely to be one of the boys (due to the neatness of the operation) and also knowing that Alex had used the restroom downstairs, my main suspect was Tristan. Lucky for him he was blissfully off to school for the day. :)

This also allowed me to come up with a plan of action. Here's how it went:

Mom: Tristan, I have some juice for you!
Tristan: It doesn't look like juice.
Mom: Well, it looks like apple juice to me. Go ahead, and drink up!
Tristan: But it's kind of yellow and green.
Mom: Yeah, that's the same as apple juice, so go ahead, you can have it.
Tristan: But...it's not juice!
Mom: You don't think it's juice?
Tristan: No
Mom: Well, I guess I'm not sure. My empty water glass was just sitting there, and then after you came in here to go potty this morning and left for school, I found it like this. It must be juice! What else would be in my glass?
Tristan: I don't know.
Mom: Well then, why don't you taste it and see?
Tristan: No! It's not juice!
Mom: What is it then?
Tristan: I don't know.
Mom: Tristan, I think you are not telling me the truth. Did you do this?

There followed a teary confession and stern lecture on lying, as well as extra chores for lying.

Despite my dismay at his lies, I found the whole situation quite humorous in a slightly disturbing way. My boys have also peed in the bathroom garbage cans. Please tell me this is normal little boy behavior!