Okay, admit it: Spending all day with your baby can be tedious at times. But things can get dull for your baby, too.
Between 3 and 6 months, an infant's vision improves dramatically, so he'll be on the lookout for new things to see, whether it's a bright light, bold pattern, or spinning ceiling fan. Even if he's just staring, if he's quiet then he's engaged.
If he gets cranky or fussy, though, he may be bored. Singing, playing peekaboo, and introducing new toys usually help, but if you're perpetually performing, your baby won't learn how to entertain himself. Give him some time to find something new to capture his attention, and then if he's still crying, try giving him a new view, suggests Lise Eliot, author of [I "What's Going On in There? How the Brain and Mind Develop in the First Five Years of Life."]
Simply moving his bouncy seat a little may do the trick -- or take him out of his seat and put him on his tummy or hold him for a while.