It's not. He might be able to eat some solids, too. Athos' could.

[ D'Artagnan sits back on the bed, letting Havoc finish the feeding. He thinks she's doing all right. She doesn't seem awkward about it, not like she had at first. He's smiling a little. ]

Just test him out with some things, don't force him. And if you want to try him with food, mash it to a pulp first. You'll get used to it.