The Englishman played the second half at Villa Park after he replaced Alex Jimenez at the break, after the Spaniard himself had come on for Adam Smith in the early stages.
Trailing by two when Cook came on, Bournemouth improved in the first 20 minutes of the second half, but after Antoine Semenyo had a penalty saved on 65 minutes, Villa regained control and scored twice more.
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Reflecting on the game, Cook said: “I think we were against a top team. I think they had a tough start to the season, we didn't, but no one should really underestimate the players they've got and they play some good football.
(Image: Nigel French/PA Wire)
“And I think it was just, we just weren’t ourselves. We weren't pressing with the intent that they were even and it showed to be honest.
“I think the second half we were a little bit more ourselves at the start and then things changed and they had a good end.”
Asked about the improvement at halftime and what Andoni Iraola had said at the break, Cook said: “I don't think he was very happy at all.
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“We really didn't show what we're about. I think the lads know that we've set such high standards for ourselves this season and in the last few seasons.
“So we've got to definitely look at that game. We've got to learn from it. And he just wanted a bit more intensity, a bit more belief and overall, just a bit more fight.”
He continued: “I don't think we're a team now that can and lose 4-0 and think it's anything but unacceptable.
“But yeah, I think we've definitely got to learn from it. It's probably come at a time where obviously players are leaving and stuff, so we've got to get back together when everyone comes back and analyse and reflect.”
Aston Villa players congratulate goalkeeper Emiliano Martinez after he saves a penalty during the Premier League match at Villa Park, Birmingham. (Image: Barrington Coombs/PA Wire)
On if the penalty save was the key turning point in the game, Cook said: “Yeah, maybe. I think besides the penalty, the first half wasn't good enough and like we said, we didn't deserve to go in at half time with a draw or winning or anything like that.
“So, yeah, stuff like that happens in football. Obviously, we've got players that have been incredible this season that have won us games. So I think it's part of football. Some go in, some don't.”