The one situation I'm thinking of right now, though, is when you're giving your kid a bottle.
I just bought a new set of bottles. (Playtex Ventaire 3-packs. The kid takes 8 oz. a couple of times a day and 6 oz. the other times, so I went ahead and got all 9 oz. bottles this round.)
It turns out the nipples are all Stage 2, with larger openings and higher flow rates. The kid could handle it most of the time, but had to catch her breath a lot, too. POINT ONE: CHECK THE SIZE/FLOW RATE
So I go out and buy a few packs of Stage 1 nipples, her normal speed, and her evening bottle nearly drives her crazy. POINT TWO: CHECK THAT THE OPENING'S OPEN. TWEAK IT OR USE A PIN TO OPEN IT.
Oh, Greg, I feel for you both. I still have the email my husband sent SEVEN YEARS AGO about a day at home with our daughter that was a horror for a couple hours because of the plugged Playtex nipple. (He was a one day a week SAHD.) Her frustration at sucking and getting nothing, his frustration at her crying and not drinking, and my horror at 8 ounces of pumped breastmilk wasted because she just took a two hour nap to console herself (she was that kind of baby) and it was the dumping out that revealed the cause.