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It is a knockout match, so perhaps we should ask the tough question. Is this a real rivalry? Pull on your criss-cross deerstalker hats, Sherlocks. Get your magnifying glass. Clasp your notebooks tight. We about to investigate.
To understand what happened between Sri Lanka and Bangladesh in the 2018 Nidahas trophy, we must roll the clock back to the previous Bangladesh Premier League, where Nazmul Islam, an unassuming slow left-arm bowler, sought to sex up his workaday act by adding a fun celebration. This is the birth of the now-infamous "Naagin dance". In Nazmul's hands, it was joyful. Innocent even. Little did he know how this was all about to blow up.

When he claimed wickets against Sri Lanka in a limited-overs series early in that year, he busted out his celebration again. Hands cocked above his head, like a cobra, a little body-thrusting action. Why wouldn't he? But then, drama. Danushka Gunathilaka did an imitation of the dance when he got a wicket in that series.

Gunathilaka might say it was all just a little bit of fun, sir, and he didn't mean anything by it. But then you can also see from the Bangladesh perspective, how it might have seemed a mockery.

So when Mushfiqur Rahim hit the winning runs in a big chase against Sri Lanka in Colombo, he did the mock-Naagin dance at Gunathilaka, who was walking past him. Other Sri Lankan players then started doing it to mock Mushfiqur, I guess? Then the whole Bangladesh team started doing it, almost in solidarity with Nazmul and Mushfiqur.

Towards the business end of the series, there was a tense game between the two sides, and after some truly wild gesticulating and on-field arguments, the Bangladesh dressing room door at the Khettarama stadium was left shattered, when they won.

If this sounds like grown men acting childish, like a little celebration being blown way out of proportion, like fans getting riled up over meaningless theatrics, or if you've got dumber reading this preview until now, all of the above are valid feelings

But we are chroniclers here at ESPNcricinfo. It is our job to present facts. Even when the facts are stupid.

More facts: these are two stupendously trash T20I teams at the moment. In this tournament, they have both been shown up by Afghanistan, whose fast bowlers decked Sri Lanka, before their spinners ran through Bangladesh. Sri Lanka have lost 10 of their last 14 T20 matches. If you think that's bad, Bangladesh have lost 14 of their last 16 completed games.

But we're in sports media, so I guess we should try hype this up. It could be close? If nothing else, these teams are evenly matched. Between Mustafizur Rahman, Taskin Ahmed and Mohammad Saifuddin, Bangladesh certainly have a more experienced seam attack. Sri Lanka perhaps have the better spinners in Wanindu Hasaranga and Maheesh Theekshana. On the batting front, Bangladesh have the experience of Shakib Al Hasan, Mahmudullah, and Mushfiqur. But the likes of Charith Asalanka and Kusal Mendis have prospered against Bangladesh in the past. There's not a lot to separate the teams

Either way, whoever wins this game advances to the Super 4 round. Whoever loses returns home much earlier than their fans would have hoped.

Form guide

(completed matches, most recent first)
Sri Lanka LWLLL
Bangladesh LLWLL

In the spotlight

Kusal Mendis has been in excellent Test-match form recently, before extending that to the shortest format, when he dominated Sri Lanka's premier T20 domestic tournament this year, shortly before setting off to the Asia Cup. He seems to have been sent up the order to open the batting in this series. Although his T20I stats are otherwise modest, this is a position he enjoys, striking at 137 when he opens, averaging 32 (career numbers are 121 and 20). He is auditioning to play this role in the T20 World Cup in October.
Amid Bangladesh's struggle in T20s over the last 12 months, Mahedi Hasan has been one of the rare consistent performers. He has the best economy rate in world cricket among bowlers who have played at least 25 innings, proving once again that orthodox offspin can still work. He brings out the side-arm deliveries from time to time, but is generally quite tight with his orthodoxy. Mahedi is also a decent hitter, and could even be used as an opener.

Pitch and conditions

It seems likely that the match will be played on a used surface, which means it might be a little more spin-friendly than tracks we have seen at this tournament. Temperatures will be scorching - likely in the low 30-degree celsius range, even in the evening.

Team news

Sri Lanka might just go in with the same XI, despite the big loss against Afghanistan. They may consider bringing the in-form Ashen Bandara into the middle order, however, perhaps in place of Danushka Gunathilaka. Or they might move Gunathilaka back up to the top of the order, and leave Pathum Nissanka out.
Sri Lanka (probable): 1 Kusal Mendis (wk), 2 Pathum Nissanka, 3 Charith Asalanka, 4 Bhanuka Rajapaksa, 5 Danushka Gunathilaka, 6 Dasun Shanaka, 7 Wanindu Hasaranga, 8 Chamika Karunaratne, 9 Maheesh Theekshana, 10 Matheesha Pathirana, 11 Dilshan Madushanka

Bangladesh have a batting quandary which could see them change the opening pair again. Mushfiqur Rahim was talked about as one of those options although he would have to agree to this unusual role. Bangladesh also could revisit their bowling attack.

Bangladesh (probable): 1 Mohammad Naim, 2 Anamul Haque, 3 Shakib Al Hasan (capt), 4 Afif Hossain, 5 Mushfiqur Rahim (wk), 6 Mahmudullah, 7 Mosaddek Hossain, 8 Mahedi Hasan, 9 Mohammad Saifuddin, 10 Taskin Ahmed, 11 Mustafizur Rahman/Nasum Ahmed

Stats and trivia

• Sri Lanka have won eight of the 12 completed matches between these teams, but lost two of the last three.

• Kusal Mendis has scores of 53, 10, 57, and 11 against Bangladesh, striking at 169 across those four innings. He has opened the batting on all those occasions, twice in Bangladesh, and twice in Colombo.

• In five innings in the UAE so far, Mahedi Hasan hasn't been particularly penetrative, taking just three wickets. But he has been economical, even if not quite up to his standards elsewhere, conceding 7.45 an over.

Quotes

"Our opening pair isn't clicking at all. We are missing Litton Das who is injured. I am hopeful the openers can bat to a plan. You can get out trying to hit the first ball, but it hurts us when nobody shows the intent. I want to see the intent. I want to see the change in mindset."
Bangladesh team director Khaled Mahmud, when asked about the possible batting improvements against Sri Lanka.