Standing in the crib!

When I put Brennan down for a nap today he played for a little while like always, but then started crying. When it didn't stop after a couple minutes, I went in there and lo and behold, I found him standing in his crib! Poor thing was so startled to see me that he fell back on his head (no injuries to report). I had him recreate it so I could take some pictures! I guess it's time to lower the mattress... where did our baby go?