Change caused by moonlight or drop in sunlight?
If Ted changes at any moon.
Some studies moonlight may've a effect on humans or plant life.
http://www.theflatearthsociety.org/forum/index.php?topic=54468.0#.Vs4GAPmLTIU
http://www.theflatearthsociety.org/forum/index.php?topic=64670.0#.Vs4KkPmLTIV
http://www.theflatearthsociety.org/forum/index.php?topic=34082.0#.Vs4O2vmLTIV
As someone said maybe UV light keeps the transformation in check.